For this task, you can get 2 points on the exam in 2020
Task 7 of the USE in biology is devoted to genetic patterns. For example, you may come across a question about hereditary variability. And first of all, you should know what this variability is - mutational, group, specific or modification, and also how different types of variability differ from each other, for example, mutational from modification. There are many options and tasks about genes and heredity: “In what marriage are children with hemophilia most often born? In unrelated, closely related, in people of different races or people of different nationalities "or" What kind of mutation is a change in the order of nucleotides in a DNA molecule?
Part of the options for task 7 of the Unified State Examination in biology contains practical questions on the topic “The influence of mutagens”. You will have to practice in advance tasks like “Determine the genotype of a child with dark straight hair if his mother has blond straight hair and his father has dark curly hair” or “There are two children in the family with lop-eared and two with normally pressed ears. Determine the genotype of their parents. To correctly solve such problems, the compiler of the FIPI tests - the Federal Institute for Pedagogical Measurements - added the appearance of gene dominance to the test conditions. So, for the last example, it will be indicated that the gene for protruding ears B is dominant over the b gene for normally closed ears.
Task number 7 of the exam in biology will be solved by you successfully if you repeat other educational material on this topic in advance. Several questions are devoted to the genetic code, several more options contain tasks in molecular biology, and they usually cause significant difficulties for schoolchildren, such as: “Determine the percentage of nucleotides with cytosine that is contained in DNA with a share of its adenine nucleotides of 10% of the total." Before the exam, you will have to carefully review this section of the textbook in order to successfully answer such questions.
MKOU"Novokayakentskaya secondary school"
from. Novokayakent
Kayakentsky district Republic of Dagestan
(for 11th grade students)
MKOU "Novokayakentskaya secondary school"
Umalatova Ravganiyat Biybulatovna
v. Novokayakent
Explanatory note
This material Preparation for the exam. Task 7. “Selecting two “drop-down” answers from five proposed answers” is recommended for students in grade 11. The material includes questions with a choice of two correct answers from five proposed answers. This material can be used to prepare for the exam. The work includes 12 questions.
Tasks: test the knowledge and ability of students to make the right choice
two outliers out of the five responses provided.
Student activities: students writing tests.
Teacher activity: providing each student with a sheet with the text of the test. Explanation of the progress of the work. Checking work. Answer analysis.
Equipment: handout with tests.
Preparation for the exam. Task 7
1. Below is a list of variability characteristics. All but two of them are used to describe the characteristics of genetic variation. Find two characteristics that “fall out” of the general series, and write down the numbers under which they are indicated in the table.
1) is characterized by changes within the gene
2) due to the combination of gametes during fertilization
3) is formed during the recombination of nenes during crossing over
4) is formed when the nucleotide sequence changes
5) due to a change in the sequence of nucleotides in the triplet
Answer:
2. All of the following characteristics, except for two, are used to describe the results of an analyzing crossing of an individual with the Aa genotype. Identify these two characteristics that “fall out” from the general list, and write down the numbers under which they are indicated in the table.
1) linkage of genes is manifested
2) the number of descendants from recessive descendants is 75%
3) the ratio of phenotypes was 1:1
4) among the streams, 50% have a dominant trait in the phenotype
5) the second parent has the genotype - aa
Answer:
3. The following concepts, except for two, are used to describe phenotypic variability. Define these two concepts that “fall out” from the general list, and write down in the table the numbers under which they are indicated.
1) not inherited
2) is adaptive
3) characteristic of a group of individuals of the species
4) limited by the reaction rate
5) due to chromosomal rearrangements
Answer:
4. All but two of the following statements are used to describe the characteristics of fertilization in angiosperms. Identify these two characteristics that “fall out” from the general list, and write down the numbers under which they are indicated in the table.
1) the egg is surrounded by a large number of sperm
2) the haploid nucleus of the gamete fuses with the diploid central cell
3) the nuclei of the female and male gametes merge
4) mobile male gametes are involved in the process
5) occurs in the embryo sac of an adult organism
Answer:
5. All of the following factors, except for two, affect the development of the human embryo. Determine these two factors that “fall out” of the general list, and write down the numbers under which they are indicated in the table.
1) the presence of polysaccharides in the shell of the fetus
2) interaction of external factors
3) genetic information in the zygote
4) interaction of parts of the embryo
5) structural features of blastomeres and blastocoel
Answer:
6. All of the following characteristics, except for two, are used to describe the nutritional characteristics of autotrophic organisms. Identify these two characteristics that “fall out” from the general list, and write down the numbers under which they are indicated in the table.
1) capture food by phagocytosis
2) use the energy released during the oxidation of inorganic substances
3) use the food contained in the food
4) synthesize organic substances from inorganic in the light
5) convert solar energy into ATP energy
Answer:
7. All but two of the terms below are used to describe genetic processes and patterns. Define these two terms that “fall out” from the general list, and write down the numbers under which they are indicated in the table.
1) rudiment
3) diheterozygous
4) divergence
5) karyotype
Answer:
8. All but two of the characteristics below are used to describe chromosomal mutations. Identify these two characteristics that “fall out” from the general list, and write down the numbers under which they are indicated in the table.
1) microevolutionary processes
2) the relationship of organisms
3) living conditions of the organism
4) patterns of individual development of the organism
5) the position of species in the system of the organic world
Answer:
10. All but two of the following statements are used to describe the similarities between plant breeding and animal breeding. Identify two positions that “fall out” of the general series, and write down in the table the numbers under which they are indicated.
1) individuals are crossed
2) self-pollination is applied
3) selection of individuals is carried out
4) polyploid forms are created
5) parental individuals are selected
Answer:
11. All but two of the positions below are used to describe the characteristics of clean lines. Identify two positions that “fall out” of the general series, and write down in the table the numbers under which they are indicated.
1) interbreeding
2) heterozygous offspring
3) homozygous recessive individuals
4) homozygous dominant individuals
5) the offspring of one self-pollinated plant
Answer:
12. Below is a list of variability characteristics. All but two are used to describe the characteristics of a genomic mutation. Find two characteristics that “fall out” of the general series, and write down the numbers under which they are indicated in the table.
1) has a group character
2) there is a loss of the Y chromosome
3) limited by the norm of the reaction of the trait
4) an additional X chromosome appears
5) the number of chromosomes is increased and a multiple of haploid
Answer:
Sources of information:
1. Unified state exam. Biology. A set of materials for the preparation of students. Tutorial. / G.S. Kalinova, L.G. Prilezhaeva.- Moscow: Intellect Center, 12017.- 168 p.
2. USE in biology. Practical training 3rd ed., revised. and additional .- St. Petersburg: BHV-Petersburg, 2017.-576 p.
4. USE. 2017. Biology. Typical test tasks / G.S. Kalinina, T.V. Mazyarkina.- M.: Exam Publishing House, 2017.- 112p.
5. Biology. Collection of problems in genetics. Basic, advanced, high level of the exam: teaching aid / Kirilenko. - 3rd edition, corrected. and additional -- Rostov n/a: Legion, 2012. – 233 p.
5. USE. Biology: typical examination options: 30 options / ed. G.S. Kalinova.-M.: National Education Publishing House, 2017.- 336 p.
Mutations are changes in the DNA of a cell. Arise under the influence of ultraviolet, radiation (X-rays), etc. They are inherited and serve as material for natural selection. differences from modifications
Gene mutations- a change in the structure of one gene. This is a change in the sequence of nucleotides: dropout, insertion, replacement, etc. For example, replacing A with T. Causes - violations during doubling (replication) of DNA. Examples: sickle cell anemia, phenylketonuria.
Chromosomal mutations– change in the structure of chromosomes: loss of a segment, doubling of a segment, rotation of a segment by 180 degrees, transfer of a segment to another (non-homologous) chromosome, etc. Causes - violations during crossing over. Example: cat cry syndrome.
Genomic mutations- change in the number of chromosomes. Causes - violations in the divergence of chromosomes.
Cytoplasmic mutations- changes in the DNA of mitochondria and plastids. They are transmitted only through the female line, because. mitochondria and plastids from spermatozoa do not enter the zygote. An example in plants is variegation.
Somatic- mutations in somatic cells (cells of the body; there may be four of the above types). During sexual reproduction, they are not inherited. They are transmitted during vegetative propagation in plants, during budding and fragmentation in coelenterates (in hydra).
The following concepts, except for two, are used to describe the consequences of a violation of the arrangement of nucleotides in a DNA region that controls protein synthesis. Define these two concepts that “fall out” from the general list, and write down the numbers under which they are indicated.
1) violation of the primary structure of the polypeptide
2) divergence of chromosomes
3) change in protein functions
4) gene mutation
5) crossing over
Choose one, the most correct option. Polyploid organisms result from
1) genomic mutations
3) gene mutations
4) combinative variability
Establish a correspondence between the characteristic of variability and its type: 1) cytoplasmic, 2) combinative
A) occurs with independent divergence of chromosomes in meiosis
B) occurs as a result of mutations in the DNA of mitochondria
B) occurs as a result of chromosome crossing
D) manifested as a result of mutations in plastid DNA
D) occurs when gametes meet by chance
Choose one, the most correct option. Down syndrome is the result of a mutation
1) genomic
2) cytoplasmic
3) chromosomal
4) recessive
Establish a correspondence between the characteristic of a mutation and its type: 1) gene, 2) chromosomal, 3) genomic
A) a change in the sequence of nucleotides in a DNA molecule
B) a change in the structure of chromosomes
C) change in the number of chromosomes in the nucleus
D) polyploidy
E) change in the sequence of genes
Choose three options. What is a genomic mutation characterized by?
1) a change in the nucleotide sequence of DNA
2) loss of one chromosome in the diploid set
3) a multiple increase in the number of chromosomes
4) a change in the structure of synthesized proteins
5) doubling a section of a chromosome
6) a change in the number of chromosomes in the karyotype
1. Below is a list of characteristics of variability. All but two of them are used to describe the characteristics of genomic variability. Find two characteristics that "drop out" of the general series, and write down the numbers under which they are indicated.
1) limited by the norm of the reaction of the sign
2) the number of chromosomes is increased and a multiple of haploid
3) an additional X chromosome appears
4) has a group character
5) there is a loss of the Y chromosome
2. All but two of the characteristics below are used to describe genomic mutations. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) violation of the divergence of homologous chromosomes during cell division
2) destruction of the fission spindle
3) conjugation of homologous chromosomes
4) change in the number of chromosomes
5) an increase in the number of nucleotides in genes
3. All but two of the characteristics below are used to describe genomic mutations. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) change in the sequence of nucleotides in a DNA molecule
2) a multiple increase in the chromosome set
3) decrease in the number of chromosomes
4) duplication of a chromosome segment
5) nondisjunction of homologous chromosomes
Choose one, the most correct option. Recessive gene mutations change
1) the sequence of stages of individual development
2) composition of triplets in a DNA segment
3) a set of chromosomes in somatic cells
4) the structure of autosomes
Choose one, the most correct option. Cytoplasmic variability is associated with the fact that
1) meiotic division is disturbed
2) mitochondrial DNA is able to mutate
3) new alleles appear in autosomes
4) gametes are formed that are incapable of fertilization
1. Below is a list of characteristics of variability. All but two of them are used to describe the characteristics of chromosomal variation. Find two characteristics that "drop out" of the general series, and write down the numbers under which they are indicated.
1) loss of a chromosome segment
2) rotation of a chromosome segment by 180 degrees
3) decrease in the number of chromosomes in the karyotype
4) the appearance of an additional X chromosome
5) transfer of a chromosome segment to a non-homologous chromosome
2. All but two of the following features are used to describe a chromosomal mutation. Identify two terms that "fall out" from the general list, and write down the numbers under which they are indicated.
1) the number of chromosomes increased by 1-2
2) one nucleotide in DNA is replaced by another
3) a section of one chromosome is transferred to another
4) there was a loss of a section of the chromosome
5) a segment of the chromosome is turned 180°
3. All but two of the characteristics below are used to describe chromosomal variation. Find two characteristics that "drop out" of the general series, and write down the numbers under which they are indicated.
1) multiplication of a segment of a chromosome several times
2) the appearance of an additional autosome
3) change in the nucleotide sequence
4) loss of the terminal section of the chromosome
5) turn of the gene in the chromosome by 180 degrees
WE FORM
1) doubling the same part of the chromosome
2) a decrease in the number of chromosomes in germ cells
3) an increase in the number of chromosomes in somatic cells
Choose one, the most correct option. What type of mutation is a change in the structure of DNA in mitochondria
1) genomic
2) chromosomal
3) cytoplasmic
4) combinative
Choose one, the most correct option. The variegation of the nocturnal beauty and snapdragon is determined by variability
1) combinative
2) chromosomal
3) cytoplasmic
4) genetic
1. Below is a list of characteristics of variability. All but two of them are used to describe the characteristics of genetic variation. Find two characteristics that "drop out" of the general series, and write down the numbers under which they are indicated.
1) due to the combination of gametes during fertilization
2) due to a change in the sequence of nucleotides in the triplet
3) is formed during the recombination of genes during crossing over
4) characterized by changes within the gene
5) is formed when the nucleotide sequence changes
2. All of the following characteristics, except for two, are the causes of gene mutation. Define these two concepts that “fall out” from the general list, and write down the numbers under which they are indicated.
1) conjugation of homologous chromosomes and exchange of genes between them
2) replacement of one nucleotide in DNA with another
3) change in the sequence of the connection of nucleotides
4) the appearance of an extra chromosome in the genotype
5) loss of one triplet in the DNA region encoding the primary structure of the protein
3. All but two of the characteristics below are used to describe gene mutations. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) replacement of a pair of nucleotides
2) the occurrence of a stop codon within the gene
3) doubling the number of individual nucleotides in DNA
4) an increase in the number of chromosomes
5) loss of a chromosome segment
4. All but two of the characteristics below are used to describe gene mutations. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) adding one triplet to DNA
2) an increase in the number of autosomes
3) change in the sequence of nucleotides in DNA
4) loss of individual nucleotides in DNA
5) multiple increase in the number of chromosomes
Choose one, the most correct option. Polyploid wheat varieties are the result of variability
1) chromosomal
2) modification
3) gene
4) genomic
Choose one, the most correct option. The production of polyploid wheat varieties by breeders is possible due to the mutation
1) cytoplasmic
2) gene
3) chromosomal
4) genomic
Establish a correspondence between characteristics and mutations: 1) genomic, 2) chromosomal. Write the numbers 1 and 2 in the correct order.
A) a multiple increase in the number of chromosomes
B) rotation of a segment of the chromosome by 180 degrees
C) exchange of sections of non-homologous chromosomes
D) loss of the central region of the chromosome
D) duplication of a section of a chromosome
E) repeated change in the number of chromosomes
Choose one, the most correct option. The appearance of different alleles of one gene occurs as a result of
1) indirect cell division
2) modification variability
3) mutation process
4) combinative variability
All but two of the terms listed below are used to classify mutations by changes in genetic material. Identify two terms that "fall out" from the general list, and write down the numbers under which they are indicated.
1) genomic
2) generative
3) chromosomal
4) spontaneous
5) gene
Establish a correspondence between the types of mutations and their characteristics and examples: 1) genomic, 2) chromosomal. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) loss or appearance of extra chromosomes as a result of a violation of meiosis
B) lead to disruption of the functioning of the gene
C) an example is polyploidy in protozoa and plants
D) doubling or loss of a chromosome segment
D) Down syndrome is a prime example.
Establish a correspondence between the categories of hereditary diseases and their examples: 1) gene, 2) chromosomal. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) hemophilia
B) albinism
B) colorblindness
D) "cat's cry" syndrome
D) phenylketonuria
Find three errors in the given text and indicate the numbers of sentences with errors.(1) Mutations are random, persistent changes in the genotype. (2) Gene mutations are the result of "mistakes" that occur in the process of doubling DNA molecules. (3) Mutations are called genomic, which lead to a change in the structure of chromosomes. (4) Many cultivated plants are polyploids. (5) Polyploid cells contain one to three extra chromosomes. (6) Polyploid plants are characterized by stronger growth and larger size. (7) Polyploidy is widely used in both plant breeding and animal breeding.
Analyze the table "Types of variability". For each cell marked with a letter, select the appropriate concept or the appropriate example from the list provided.
1) somatic
2) gene
3) replacement of one nucleotide with another
4) duplication of a gene in a region of the chromosome
5) addition or loss of nucleotides
6) hemophilia
7) color blindness
8) trisomy in the chromosome set
Down syndrome: causes, symptoms, diagnosis and treatment
Down syndrome is a genetic anomaly resulting from the bifurcation of one of the 21 chromosomes, as a result of which the human chromosome set includes not 46, but 47 chromosomes, which causes further clinical signs.
The phenomenon was first described by the English physician John Down (thanks to whom the syndrome got its name) in 1866 as mental retardation with characteristic external signs, but only in 1959 did the French geneticist Jerome Lejeune determine the relationship between an excess number of chromosomes and the symptoms of the syndrome.
Today, despite the high development of medical technology, Down syndrome is a very common and not fully understood phenomenon, which gives rise to many different myths, sometimes contradicting each other. However, it is known that:
- This anomaly is equally common in both sexes, different ethnic groups and nationalities.
- The development of the syndrome does not depend on the lifestyle of the parents and has a genetic “origin”, when anomalies occur either at the stage of formation of an egg or sperm (it is not excluded, but it is practically unlikely that they can be affected by harmful environmental factors), or during the fusion of sex cells after fertilization.
- The syndrome occurs during pathological processes in the genes, when another 1 chromosome joins the 21st pair (therefore, they get 47 instead of 46). Most often this is due to the fact that during cell division, the chromosomes do not diverge. In addition, one of the main reasons may be the heredity of the mutation of the 21st chromosome - when this chromosome merges with another. This mutation is called trisomy and occurs in about one in 800 newborns, and 88% of cases are due to the "non-disjunction" of female gametes (reproductive cells).
- Down syndrome is a common pathology that has 3 forms (hereditary disease, mutation of the 21st chromosome, mosaic disease) and 4 degrees of the disease:
- weak - patients practically do not differ from ordinary children, quite often they successfully adapt in society and can occupy a very prestigious place in society;
- average;
- heavy;
- deep - children cannot lead the generally accepted way of life of society, and this greatly complicates the life of parents. Nowadays, there is a special prenatal diagnosis that allows you to find out in time about the likelihood of developing a pathology. If you suspect Down's syndrome, parents face the question: leave the child or get rid of the pregnancy? At the birth of a baby, others will arise: how to raise a child, how to provide him with a normal life and at the same time live fully on his own?
- Trisomy is a subspecies of the syndrome, characterized by the formation of three chromosomes in 21 pairs. This phenomenon has been little studied, but there is a version that the age of the mother plays a significant role here: the older the woman, the more likely it is to give birth to a baby with Down syndrome. This is due to the age of the egg, when the birth of a gamete is possible not with 23, but with 24 chromosomes. In this case, when a cell is fertilized by a male gamete with 23 chromosomes, one remains superfluous, and a mutation occurs: the chromosome sticks (attaches) to 21 pairs. As a result, all cells of the fetus will contain 47 chromosomes.
- Mosaicism is a rare phenomenon (they make up only 1-2% of all cases), in which not all cells of the fetus will contain an abnormal number of chromosomes, therefore only certain organs and tissues are affected by the phenomenon of the syndrome (if copying falls on the genes responsible for mental and motor development , then the development of the syndrome in the fetus cannot be avoided). This is due to the "non-disjunction" of the chromosome series not at the stage of formation of parent germ cells, but at the early stages of development of the embryo. This form of the syndrome - with a smoothed clinical picture - is mild, but during perinatal studies it is extremely difficult to diagnose.
- Translocation - occurs during cell fusion and in this case, a shift of part of one chromosome in the 21st pair to the side of the other chromosome is noted.
- The age of the parents is too young a girl, or, conversely, a woman over 40 years old, and for men - over 45 years old (the risk of having a child with the syndrome is 1:30). Due to age, the maturation and division of chromosomes “slow down”, and a defective cell is obtained. Being involved in fertilization, it will subsequently become the cause of the development of Down syndrome.
- Closely related marriage (bond).
- Folic acid deficiency during pregnancy.
- The likelihood of having a child with Down syndrome increases if the disease occurs in the family of the parents.
- narrow and slanting (Mongoloid) eyes (previously the pathology was called "Mongolism");
- the presence of an epicanthus (a special fold at the inner corner of the eye, which covers the lacrimal tubercle and does not pass to the upper eyelid);
- strabismus and noticeable pigmentation of the iris (Brushfield spots), cataracts are possible;
- flat profile - flat and wide bridge of the nose and short nose, occipital region;
- shortened (small) skull;
- shortened neck - the newborn has a fold of skin in this area;
- underdeveloped auricles;
- hypotension (weak tone) of the muscles;
- an arched palate, an abnormally large tongue (macroglossia) and an open mouth due to reduced muscle tone;
- wide hands with short fingers due to underdevelopment of the middle phalanges - there is a curvature in the little finger,
- on the palms there is a single transverse fold;
- short limbs;
- there is a deformation (keeled or funnel-shaped) of the chest;
- often (about 40%) children with the syndrome are born with congenital heart disease (defective processes in the septum between the ventricle), which is one of the main causes of their mortality;
- pathological processes of the gastrointestinal tract (for example, duodenal artesia);
- the child may be born with leukemia;
- the child lags behind in growth, mental development;
- hoarse voice;
- most often, patients are infertile, but when offspring appear, children have the same pathology.
- thickening of the collar space (with a developing syndrome, it will be more than 3 mm);
- absence of the nasal bone;
- small sizes of the frontal lobe and cerebellum (hypoplasia);
- shortened femurs and ulnas, etc.
- choriobiopsy - a study of the tissues of the fetal membrane;
- amniocetesis (analysis of amniotic fluid) - the study of the cellular composition of amniotic fluid, as well as baby tissues, which will provide information about the cellular set of chromosomes of the child;
- cordocentesis - analysis of the umbilical cord blood of the fetus.
- Piracetam, Aminolone, Cerebrolysin - to normalize blood circulation in the brain;
- neurostimulators;
- vitamin complexes - to improve overall health.
5. Down syndrome is not recommended to be called a disease, since people living with this syndrome, although they have pathological changes that prevent them from realizing their full potential, nevertheless, with the right approach of specialists from an early age, most are able to adapt quite well in society.
Causes of the development of Down syndrome
As we have already said, Down syndrome occurs due to an anomaly in cell division, when another third chromosome is glued to the 21st pair of chromosomes. In other words, it is a congenital pathology that cannot be obtained in the course of life. The causes of chromosomal disorders are very difficult to establish.
This happens as a result of 3 forms of pathology that have an almost identical clinical picture of this syndrome:
However, there are other reasons for the development of Down syndrome:
Down Syndrome Symptoms
The disease is usually called a syndrome, since it is characterized by a number of symptoms and signs, as well as characteristic manifestations:
However, it is worth noting that people with Down syndrome rarely have malignant tumors, and this is due to the protection of the extra gene.
At the birth of twins, the syndrome is observed in both children.
The severity of the above symptoms in all patients is different.
Diagnosis of Down syndrome
The modern level of medicine and technology in case of suspected Down syndrome allows for timely diagnosis and, if DNA abnormalities are detected, get rid of the current pregnancy.
For diagnosis, several methods are used:
1. Ultrasound - carried out in the 2nd or 3rd trimester of pregnancy, when a fetus is scanned to detect pathology. This method makes it possible to "see" the signs of Down syndrome with the help of some "measurements":
However, ultrasound reveals only one of the forms of the syndrome - trisomy. The remaining subspecies of pathology cannot be detected by this diagnostic method.
2. Biochemical analysis of the blood of a pregnant woman in the 1st trimester (to establish the karyotype - the gene content of the mother's blood), during which the level of the hormone synthesized by the fetus (hCG) and PAPP-A is taken into account. In the 2nd trimester, the analysis is carried out again.
3. A biochemical test (by the level of free chorionic hormone) makes it possible to diagnose Down syndrome as early as the 12th week of pregnancy, and at the 16th week, a test for estriol and α-faetoprotein is carried out - indicators of the presence of Down syndrome. When confirming the data, you must immediately contact a geneticist who prescribes:
These methods are highly accurate, but, unfortunately, unsafe for a woman - they can lead to complications, up to miscarriage, and therefore are carried out only in extreme cases (if the pregnant woman is over 35 years old, if there is a suspicion of a syndrome in ultrasound studies, or there is a disease in family).
However, science does not stand still, and London clinics have already developed a special test that allows you to accurately find out about all genetic diseases.
After the birth of a child, all the signs of Down syndrome are clearly visible and obvious, but genetic tests are done to confirm (this is necessary to exclude the possibility of developing another disease). It should be noted that not all of the symptoms described above must be present in every sick child - an individual baby may have his own set.
With age, the symptoms worsen, and other ailments may develop - obesity, weakened immunity (and these are frequent colds and infectious diseases), cataracts, lag in the development of the nervous system, mental abilities and speech.
Down syndrome treatment
Down syndrome is an incurable disease, since no one can “correct” DNA, but it is possible to improve the general condition of the patient and improve his quality of life.
Treatment of congenital pathologies is carried out by specialists - a pediatrician, a cardiologist, a gastroenterologist, an ophthalmologist and others. Their efforts are aimed at improving the health of the patient, and despite the fact that there is no specific treatment for the syndrome, it is still impossible to avoid taking medications. Among them:
However, quite often, with age, children with Down syndrome show a number of complications associated with physical health: diseases of the heart and digestive organs, disorders of the endocrine and immune systems, problems with hearing, sleep, vision, and cases of respiratory arrest are not uncommon. In addition, almost a quarter of patients after 40 years of age (and sometimes even earlier) have obesity, epilepsy, Alzheimer's disease and leukemia. At the same time, it is difficult to predict how the disease will develop, because everything depends on the individual characteristics of the organism, the degree of the disease and the activities with the child. Few people with Down syndrome live to be 50 years old.
At the same time, a speech therapist, a neuropathologist and other specialists deal with the elimination of significant disorders of verbal and motor functions, intellectual retardation; self-care skills training. Based on this, children with Down syndrome are recommended to be sent to specialized educational institutions.
To correct mental retardation, specially designed training programs are used, and it is worth noting that mental and cognitive symptoms in each individual case are expressed differently.
Depending on the degree of damage and the treatment (training with the child), a significant reduction in developmental delay can be achieved. With regular activities with the baby, he is able to learn to walk, talk, write and serve himself. Children with Down syndrome can attend public schools, go to college, get married, and in some cases even have children of their own.
Among people with Down syndrome there are a lot of artists, writers, artists. There is even an opinion that the “children of the sun” are not just a genetic disease, but a separate “species” of people who not only differ in the presence of an “extra” chromosome, but live according to their own moral laws and have their own principles.
People with Down syndrome are often referred to as "children of the sun" or "sunshine" because they are constantly smiling, gentle, kind, and radiate warmth. In 2006, the International Down Syndrome Day was established, which is celebrated around the world on March 21.
14 more articles on the topic: Special children
Down syndrome: doctor's explanation
Children with Down syndrome in our country are treated ambiguously. Many consider this disease to be synonymous with profound retardation. However, this is a misconception: children with Down syndrome can go to school, learn new things and live a vibrant and fulfilling life. The presence of a diagnosis is not a sentence for the parents and the baby. People living side by side with such children should help them and actively involve them in their environment - after all, everyone is equal in the desire to be happy!
History
People tend to consider Down syndrome to be a severe neurological disease accompanied by mental retardation. They are not even afraid of the pathology itself, but the unknown. Therefore, it is necessary to talk about what Down syndrome is.
Pathology has been known for centuries. If you look closely at the canvases of medieval artists, you can notice people with special needs on them. Similar characters are described in works of art. But the true nature of the syndrome was studied only in the twentieth century, when chromosomes, genes and the structure of DNA were discovered.
Today it is reliably known that Down syndrome is formed in the presence of an anomaly in the chromosome set of cells, this is the so-called trisomy of 21 pairs of chromosomes. This means that in this pair, as a result of a mutation, an extra chromosome arose. Thus, these children have not 46, but 47 chromosomes in their cells. With Down syndrome, numerous variations are possible - from an entire extra chromosome to part of it, which makes the defects very different.
Why it happens
In the human body, cells of all organs and tissues undergo division. Including the division of sex cells - eggs and sperm. In all cells of the body, equal division must occur so that the daughter cells are absolutely identical. But nature is not perfect and can fail under the influence of any adverse factors. Then in one of the cells there is one more chromosome in the 17th pair, and with the participation of such a cell in conception, a child with Down syndrome may be born.
Down syndrome is not one pathology, but a whole group of conditions similar in mechanisms and course, united by a common name. In the vast majority of cases, the extra chromosome will be present in all cells of the body. Less often, options arise when an extra chromosome moves to the region of 22 pairs or 14 pairs of chromosomes. There may also be a mosaic variant of the syndrome, in which, along with cells that have a defect in 21 pairs of chromosomes, there are also completely normal cells with 46 chromosomes. Isolation of such groups of defects in cells is carried out for a reason. The prognosis will also depend on which form is detected in a child: how severe external and internal disorders will be, how and how it will differ from other children.
The mechanism of the appearance of the syndrome
Down syndrome refers to a genetic pathology that is formed in the fetus at the time of its conception, if a defective egg and sperm merge. In about 90% of cases, the cause is a defective egg with 24 chromosomes instead of 23, and in about 10% it can be a defective sperm. The formation of such defective germ cells can be influenced by illnesses of the mother or father, stress, the presence of bad habits, inadequate and irrational nutrition, everything that in one way or another can affect the division of germ cells. But the course of pregnancy and childbirth does not affect the development of Down syndrome.
The fact that germ cells will contain an extra chromosome will be guilty of a special protein of the cells. It has the function of stretching chromosomes to the poles of the cell during division, so that as a result each of the cells receives equal genetic information. If the protein has a defect, then on one side the microtubule pulling the chromosome will be thin and defective, and a stronger tube from another cell that is being formed will pull it towards itself, to the opposite pole. After that, the cells begin to separate from each other, turning into two full-fledged formations - but one will have 22 chromosomes, and the other - 24. This defective cell can give life to a baby with Down syndrome.
Similar problems can arise when exposed to the following factors:
● closely related marriages carrying the same mutations. The closer the degree of relationship, the more likely the mutation;
● pregnancy before the age of 18, as the body is not yet mature, and there may be defects in cell division;
● late pregnancy: after 35 years (for women) and after 45 years (for men) with the accumulation of a load of mutations;
● carriage of defects in 21 pairs of chromosomes.
But for the most part, having Down syndrome is the result of a spontaneous mutation for which no one is to blame.
External features of children with Down syndrome
Children with Down syndrome can usually be identified from birth. Their face is somewhat flattened, the eyes are slightly slanted, and the head has a specific shape, while the mouth is small. The child's tongue appears large and may not fit in the mouth, causing it to protrude slightly. Gradually, this feature disappears. The palms of the crumbs are wide, the fingers are short with the little finger bent inward. Typical transverse single folds are observed on the palms. But by appearance, the diagnosis is not made. Doctors must conduct a full genetic examination to confirm or refute preliminary suspicions.
Health problems in children
Due to the characteristics of chromosomes, children with this syndrome may have health problems. From birth, they develop mild or moderate muscle hypotension, which gradually disappears as they grow. These babies are usually born small and small in stature compared to their peers, but with regular care and proper exercise, they can grow and gain weight almost like other children. Particular attention should be paid to the internal organs, their structure and work: children with Down syndrome often have hearing problems, sleep apnea syndromes, and disorders of the endocrine system. An extra chromosome gives heart defects and development of the abdominal organs, which may require the intervention of doctors up to surgery.
The development of the nervous system has a special mechanism
Because of the extra chromosome, the nervous system works and develops according to its own scenario. It is these features that will underlie the formation of mental and physical development delays. In children, there may be a violation of the circulation of cerebrospinal fluid, which leads to its excessive formation in the region of the vascular ventricles of the brain in case of malabsorption. This can lead to increased intracranial pressure. There may be focal lesions in the area of peripheral nerves and the brain, which gives a violation of coordination and coordination of movements and can inhibit the development of motor skills - fine and large. The cerebellum is usually smaller than normal, does not perform its functions actively enough, which leads to a weakening of muscle tone, difficulties in controlling one's body in space and controlling the coordination of movements. There may be cerebrovascular accidents due to ligament weakness and instability in the cervical spine. The volume of the brain can be reduced and the size of the ventricles is increased, the activity of the cortex decreases, which leads to a decrease in the number of nerve impulses with lethargy, slowness, and a decrease in the speed of the thought process. But this does not mean at all that children are unteachable and severely disabled, they just do everything more slowly and it will take more time for them to learn.
Development of children with Down syndrome
Children with this syndrome learn skills later - they also learn to walk, talk, use objects and use the toilet. The child will be able to learn to do almost everything that other children do, just the timing of learning the skills will be individual. They usually begin to smile between two and four months, roll over on their stomach between 4 and 18 months, sit on their own between 6 and 28 months, crawl between 7 and 20 months, attempt to walk between 12 and 60 months, talk at 9 up to 30 months. For such children, full-fledged care and breastfeeding are important, this will help to improve health and increase immunity, and the formation of the right skills for the baby. During feeding, especially close and intimate bonds will be established between mother and baby, which will bring a lot of joy to both.
Treatment and rehabilitation
Unfortunately, today it is impossible to save a child from Down syndrome. Scientists do not know how to correct the genetic errors of cells and chromosomal abnormalities. But teachers, doctors and parents can make the life of such children bright, healthy and long. Babies with this syndrome will not necessarily be sick, despite the fact that they can catch a cold more often than other children or have pathologies of internal organs. Malformations today are already able to be corrected, hearing and immunity problems are solvable, and endocrine abnormalities are corrected.
The biggest problem of such families is the attitude of society towards them, as well as the attitude of relatives. A child with Down syndrome can be born in any family, regardless of wealth, race, country of residence and other conditions, as well as the age of the parents. The main thing you need to know is that children with Down syndrome are complete and trainable. Moreover, they are very talented and can teach others a lot. They can teach kindness, openness and sincerity, which everyone so often lacks!
Alena Paretskaya, pediatrician
Mutations are changes in the DNA of a cell. Arise under the influence of ultraviolet, radiation (X-rays), etc. They are inherited and serve as material for natural selection. differences from modifications
Gene mutations- a change in the structure of one gene. This is a change in the sequence of nucleotides: dropout, insertion, replacement, etc. For example, replacing A with T. Causes - violations during doubling (replication) of DNA. Examples: sickle cell anemia, phenylketonuria.
Chromosomal mutations– change in the structure of chromosomes: loss of a segment, doubling of a segment, rotation of a segment by 180 degrees, transfer of a segment to another (non-homologous) chromosome, etc. Causes - violations during crossing over. Example: cat cry syndrome.
Genomic mutations- change in the number of chromosomes. Causes - violations in the divergence of chromosomes.
- polyploidy– multiple changes (several times, for example, 12 → 24). It does not occur in animals, in plants it leads to an increase in size.
- Aneuploidy- changes on one or two chromosomes. For example, one extra twenty-first chromosome leads to Down syndrome (while the total number of chromosomes is 47).
Cytoplasmic mutations- changes in the DNA of mitochondria and plastids. They are transmitted only through the female line, because. mitochondria and plastids from spermatozoa do not enter the zygote. An example in plants is variegation.
Somatic- mutations in somatic cells (cells of the body; there may be four of the above types). During sexual reproduction, they are not inherited. They are transmitted during vegetative propagation in plants, during budding and fragmentation in coelenterates (in hydra).
The following concepts, except for two, are used to describe the consequences of a violation of the arrangement of nucleotides in a DNA region that controls protein synthesis. Define these two concepts that “fall out” from the general list, and write down the numbers under which they are indicated.
1) violation of the primary structure of the polypeptide
2) divergence of chromosomes
3) change in protein functions
4) gene mutation
5) crossing over
Choose one, the most correct option. Polyploid organisms result from
1) genomic mutations
3) gene mutations
4) combinative variability
Establish a correspondence between the characteristic of variability and its type: 1) cytoplasmic, 2) combinative
A) occurs with independent divergence of chromosomes in meiosis
B) occurs as a result of mutations in the DNA of mitochondria
B) occurs as a result of chromosome crossing
D) manifested as a result of mutations in plastid DNA
D) occurs when gametes meet by chance
Choose one, the most correct option. Down syndrome is the result of a mutation
1) genomic
2) cytoplasmic
3) chromosomal
4) recessive
Establish a correspondence between the characteristic of a mutation and its type: 1) gene, 2) chromosomal, 3) genomic
A) a change in the sequence of nucleotides in a DNA molecule
B) a change in the structure of chromosomes
C) change in the number of chromosomes in the nucleus
D) polyploidy
E) change in the sequence of genes
Choose three options. What is a genomic mutation characterized by?
1) a change in the nucleotide sequence of DNA
2) loss of one chromosome in the diploid set
3) a multiple increase in the number of chromosomes
4) a change in the structure of synthesized proteins
5) doubling a section of a chromosome
6) a change in the number of chromosomes in the karyotype
1. Below is a list of characteristics of variability. All but two of them are used to describe the characteristics of genomic variability. Find two characteristics that "drop out" of the general series, and write down the numbers under which they are indicated.
1) limited by the norm of the reaction of the sign
2) the number of chromosomes is increased and a multiple of haploid
3) an additional X chromosome appears
4) has a group character
5) there is a loss of the Y chromosome
2. All but two of the characteristics below are used to describe genomic mutations. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) violation of the divergence of homologous chromosomes during cell division
2) destruction of the fission spindle
3) conjugation of homologous chromosomes
4) change in the number of chromosomes
5) an increase in the number of nucleotides in genes
3. All but two of the characteristics below are used to describe genomic mutations. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) change in the sequence of nucleotides in a DNA molecule
2) a multiple increase in the chromosome set
3) decrease in the number of chromosomes
4) duplication of a chromosome segment
5) nondisjunction of homologous chromosomes
Choose one, the most correct option. Recessive gene mutations change
1) the sequence of stages of individual development
2) composition of triplets in a DNA segment
3) a set of chromosomes in somatic cells
4) the structure of autosomes
Choose one, the most correct option. Cytoplasmic variability is associated with the fact that
1) meiotic division is disturbed
2) mitochondrial DNA is able to mutate
3) new alleles appear in autosomes
4) gametes are formed that are incapable of fertilization
1. Below is a list of characteristics of variability. All but two of them are used to describe the characteristics of chromosomal variation. Find two characteristics that "drop out" of the general series, and write down the numbers under which they are indicated.
1) loss of a chromosome segment
2) rotation of a chromosome segment by 180 degrees
3) decrease in the number of chromosomes in the karyotype
4) the appearance of an additional X chromosome
5) transfer of a chromosome segment to a non-homologous chromosome
2. All but two of the following features are used to describe a chromosomal mutation. Identify two terms that "fall out" from the general list, and write down the numbers under which they are indicated.
1) the number of chromosomes increased by 1-2
2) one nucleotide in DNA is replaced by another
3) a section of one chromosome is transferred to another
4) there was a loss of a section of the chromosome
5) a segment of the chromosome is turned 180°
3. All but two of the characteristics below are used to describe chromosomal variation. Find two characteristics that "drop out" of the general series, and write down the numbers under which they are indicated.
1) multiplication of a segment of a chromosome several times
2) the appearance of an additional autosome
3) change in the nucleotide sequence
4) loss of the terminal section of the chromosome
5) turn of the gene in the chromosome by 180 degrees
WE FORM
1) doubling the same part of the chromosome
2) a decrease in the number of chromosomes in germ cells
3) an increase in the number of chromosomes in somatic cells
Choose one, the most correct option. What type of mutation is a change in the structure of DNA in mitochondria
1) genomic
2) chromosomal
3) cytoplasmic
4) combinative
Choose one, the most correct option. The variegation of the nocturnal beauty and snapdragon is determined by variability
1) combinative
2) chromosomal
3) cytoplasmic
4) genetic
1. Below is a list of characteristics of variability. All but two of them are used to describe the characteristics of genetic variation. Find two characteristics that "drop out" of the general series, and write down the numbers under which they are indicated.
1) due to the combination of gametes during fertilization
2) due to a change in the sequence of nucleotides in the triplet
3) is formed during the recombination of genes during crossing over
4) characterized by changes within the gene
5) is formed when the nucleotide sequence changes
2. All of the following characteristics, except for two, are the causes of gene mutation. Define these two concepts that “fall out” from the general list, and write down the numbers under which they are indicated.
1) conjugation of homologous chromosomes and exchange of genes between them
2) replacement of one nucleotide in DNA with another
3) change in the sequence of the connection of nucleotides
4) the appearance of an extra chromosome in the genotype
5) loss of one triplet in the DNA region encoding the primary structure of the protein
3. All but two of the characteristics below are used to describe gene mutations. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) replacement of a pair of nucleotides
2) the occurrence of a stop codon within the gene
3) doubling the number of individual nucleotides in DNA
4) an increase in the number of chromosomes
5) loss of a chromosome segment
4. All but two of the characteristics below are used to describe gene mutations. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) adding one triplet to DNA
2) an increase in the number of autosomes
3) change in the sequence of nucleotides in DNA
4) loss of individual nucleotides in DNA
5) multiple increase in the number of chromosomes
Choose one, the most correct option. Polyploid wheat varieties are the result of variability
1) chromosomal
2) modification
3) gene
4) genomic
Choose one, the most correct option. The production of polyploid wheat varieties by breeders is possible due to the mutation
1) cytoplasmic
2) gene
3) chromosomal
4) genomic
Establish a correspondence between characteristics and mutations: 1) genomic, 2) chromosomal. Write the numbers 1 and 2 in the correct order.
A) a multiple increase in the number of chromosomes
B) rotation of a segment of the chromosome by 180 degrees
C) exchange of sections of non-homologous chromosomes
D) loss of the central region of the chromosome
D) duplication of a section of a chromosome
E) repeated change in the number of chromosomes
Choose one, the most correct option. The appearance of different alleles of one gene occurs as a result of
1) indirect cell division
2) modification variability
3) mutation process
4) combinative variability
All but two of the terms listed below are used to classify mutations by changes in genetic material. Identify two terms that "fall out" from the general list, and write down the numbers under which they are indicated.
1) genomic
2) generative
3) chromosomal
4) spontaneous
5) gene
Establish a correspondence between the types of mutations and their characteristics and examples: 1) genomic, 2) chromosomal. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) loss or appearance of extra chromosomes as a result of a violation of meiosis
B) lead to disruption of the functioning of the gene
C) an example is polyploidy in protozoa and plants
D) doubling or loss of a chromosome segment
D) Down syndrome is a prime example.
Establish a correspondence between the categories of hereditary diseases and their examples: 1) gene, 2) chromosomal. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) hemophilia
B) albinism
B) colorblindness
D) "cat's cry" syndrome
D) phenylketonuria
Find three errors in the given text and indicate the numbers of sentences with errors.(1) Mutations are random, persistent changes in the genotype. (2) Gene mutations are the result of "mistakes" that occur in the process of doubling DNA molecules. (3) Mutations are called genomic, which lead to a change in the structure of chromosomes. (4) Many cultivated plants are polyploids. (5) Polyploid cells contain one to three extra chromosomes. (6) Polyploid plants are characterized by stronger growth and larger size. (7) Polyploidy is widely used in both plant breeding and animal breeding.
Analyze the table "Types of variability". For each cell marked with a letter, select the appropriate concept or the appropriate example from the list provided.
1) somatic
2) gene
3) replacement of one nucleotide with another
4) duplication of a gene in a region of the chromosome
5) addition or loss of nucleotides
6) hemophilia
7) color blindness
8) trisomy in the chromosome set
Heredity and variability. Chromosomal theory of heredity
Heredity- this is the most important feature of living organisms, which consists in the ability to transfer the properties and functions of parents to descendants. This transmission is carried out with the help of genes.
A gene is a unit of storage, transmission and realization of hereditary information. A gene is a specific section of a DNA molecule, in the structure of which the structure of a certain polypeptide (protein) is encoded. Probably, many DNA regions do not encode proteins, but perform regulatory functions. In any case, in the structure of the human genome, only about 2% of DNA are sequences on the basis of which messenger RNA is synthesized (transcription process), which then determines the amino acid sequence during protein synthesis (translation process). It is currently believed that there are about 30,000 genes in the human genome.
Genes are located on chromosomes, which are located in the nuclei of cells and are giant DNA molecules.
Chromosomal theory of heredity was formulated in 1902 by Setton and Boveri. According to this theory, chromosomes are carriers of genetic information that determines the hereditary properties of an organism. In humans, each cell has 46 chromosomes, divided into 23 pairs. Chromosomes that form a pair are called homologous.
Sex cells (gametes) are formed using a special type of division - meiosis. As a result of meiosis, only one homologous chromosome from each pair remains in each germ cell, i.e. 23 chromosomes. Such a single set of chromosomes is called haploid. At fertilization, when the male and female sex cells merge and a zygote is formed, the double set, which is called diploid, is restored. In the zygote of the organism that develops from it, one chromosome from each nara is received from the paternal organism, the other from the maternal one.
A genotype is a set of genes received by an organism from its parents.
Another phenomenon that genetics studies is variability. Under the variability understand the ability of organisms to acquire new features - differences within the species. There are two types of change:
- hereditary;
- modification (non-hereditary).
hereditary variability- this is a form of variability caused by changes in the genotype, which may be associated with mutational or combinative variability.
mutational variability.
Genes undergo changes from time to time, which are called mutations. These changes are random and appear spontaneously. The causes of mutations can be very diverse. There are a number of factors that increase the likelihood of a mutation occurring. This may be exposure to certain chemicals, radiation, temperature, etc. Mutations can be caused by these means, but the random nature of their occurrence remains, and it is impossible to predict the appearance of a particular mutation.
The resulting mutations are transmitted to descendants, that is, they determine hereditary variability, which is associated with where the mutation occurred. If a mutation occurs in a germ cell, then it has the opportunity to be transmitted to descendants, i.e. be inherited. If the mutation occurred in a somatic cell, then it is transmitted only to those of them that arise from this somatic cell. Such mutations are called somatic, they are not inherited.
There are several main types of mutations.
- Gene mutations, in which changes occur at the level of individual genes, i.e. sections of the DNA molecule. This can be a waste of nucleotides, the replacement of one base with another, a rearrangement of nucleotides, or the addition of new ones.
- Chromosomal mutations associated with a violation of the structure of chromosomes lead to serious changes that can be detected using a microscope. Such mutations include loss of chromosome sections (deletions), addition of sections, rotation of a chromosome section by 180°, and the appearance of repeats.
- Genomic mutations are caused by a change in the number of chromosomes. Extra homologous chromosomes may appear: in the chromosome set, in place of two homologous chromosomes, there are three trisomy. In the case of monosomy, there is a loss of one chromosome from a pair. With polyploidy, a multiple increase in the genome occurs. Another variant of genomic mutation is haploidy, in which only one chromosome from each pair remains.
The frequency of mutations is affected, as already mentioned, by a variety of factors. When a number of genomic mutations occur, the age of the mother, in particular, is of great importance.
Combination variability.
This type of variability is determined by the nature of the sexual process. With combinative variability, new genotypes arise due to new combinations of genes. This type of variability is manifested already at the stage of formation of germ cells. As already mentioned, each sex cell (gamete) contains only one homologous chromosome from each pair. Chromosomes enter the gamete randomly, so the germ cells of one person can differ quite a lot in the set of genes in the chromosomes. An even more important stage for the emergence of combinative variability is fertilization, after which in a newly emerged organism 50% of the genes are inherited from one parent, and 50% from the other.
Modification variability is not associated with changes in the genotype, but is caused by the influence of the environment on the developing organism.
The presence of modification variability is very important for understanding the essence of inheritance. Traits are not inherited. You can take organisms with exactly the same genotype, for example, grow cuttings from the same plant, but place them in different conditions (light, humidity, mineral nutrition) and get quite different plants with different traits (growth, yield, leaf shape). etc.). To describe the actually formed signs of an organism, the concept of "phenotype" is used.
The phenotype is the whole complex of actually occurring signs of an organism, which is formed as a result of the interaction of the genotype and environmental influences in the course of the development of the organism. Thus, the essence of inheritance lies not in the inheritance of a trait, but in the ability of the genotype, as a result of interaction with developmental conditions, to give a certain phenotype.
Since modification variability is not associated with changes in the genotype, modifications are not inherited. Usually this position is for some reason difficult to accept. It seems that if, say, parents train for several generations in lifting weights and have developed muscles, then these properties must be passed on to children. Meanwhile, this is a typical modification, and training is the environmental impact that influenced the development of the trait. No changes in the genotype occur during modification, and the traits acquired as a result of modification are not inherited. Darwin called this kind of variation non-hereditary.
To characterize the limits of modification variability, the concept of the reaction norm is used. Some traits in a person cannot be changed due to environmental influences, such as blood type, gender, eye color. Others, on the contrary, are very sensitive to the effects of the environment. For example, as a result of prolonged exposure to the sun, the skin color becomes darker, and the hair lightens. The weight of a person is strongly influenced by dietary habits, illness, the presence of bad habits, stress, lifestyle.
Environmental influences can lead not only to quantitative, but also to qualitative changes in the phenotype. In some species of primrose, at low air temperatures (15-20 C), red flowers appear, but if the plants are placed in a humid environment with a temperature of 30 ° C, then white flowers form.
moreover, although the reaction rate characterizes a non-hereditary form of variability (modification variability), it is also determined by the genotype. This provision is very important: the reaction rate depends on the genotype. The same influence of the environment on the genotype can lead to a strong change in one of its traits and not affect the other in any way.
Changing the genome of a cell can be carried out in three ways: as a result of a change in the number of chromosomes, the number and order of genes, or due to changes in individual genes. When the number of chromosomes changes (the so-called genomic mutations), one or more chromosomes can be lost or acquired (aneuploidy), or the number of sets of chromosomes can change (polyploidy). Polyploidy plays an important role in the evolution of plants and is widely used in their selection and development of new varieties. In animals, polyploidy, as a rule, is lethal, because it violates the chromosomal mechanism for determining sex.
A change in the arrangement of genes in chromosomes (the so-called chromosomal mutations) occurs as a result of duplication (repetition) of a gene, inversion (flip of one or several genes by 180 °), translocation, or transposition (transfer of a chromosome region commensurate in length with the gene to a new position in the same or on another chromosome), as well as deletions - loss of a section of genetic material (from several nucleotide pairs to fragments containing several genes; a special case of deficiency is a lack of genes at the end of the chromosome). When a number of genes are translocated, the so-called effect of the position of the gene is observed - a change in the manifestation of the activity of the gene when it moves to another part of the chromosome. This explains, for example, the appearance of striped eyes in Drosophila.
Mutations (from lat. mutatio - change), sudden (jump-like) natural or artificially induced inherited changes in the genetic material (genome), leading to a change in certain signs of the organism. There are generative mutations that occur in germ cells and are inherited, and somatic mutations that form in cells that do not participate in reproduction (somatic cells). Somatic mutations lead to the emergence of genetic mosaics, i.e., to a change in some part of the organism that develops from a mutant cell. In plants, somatic mutations are transferred to offspring if the plants are propagated not by seeds, but by somatic parts of the body (for example, cuttings, buds, tubers).
genetic damage
genetic damage – these are inherited damage to the genetic code in germ cells. It is known that the elementary unit of heredity is the gene, which has a strictly defined structure and function. All genes of a cell of an organism create a common genotype of an individual and thereby ensure the vital activity of the organism as a whole.
Chemically, a gene is a section of a DNA molecule. The order of combination in the gene of nitrogenous bases - adenine, thymine, cytosine and guanine - determines its specificity and code. With the help of a code, a gene transmits strictly defined information for the development of a particular function or structure of the cell and the organism as a whole. Genes are embedded in the structure of chromosomes. Each cell of the human body contains 23 pairs of chromosomes, 22 of which are common, and the last determines the male (XY) or female (XX) sex of a person. In the process of fertilization, the germ cells merge into one, the nucleus of which already has two sets of chromosomes. During subsequent division, each chromosome forms its exact copy. Therefore, daughter cells will have exactly the same number and structure of chromosomes and genes, i.e. the daughter cells will be copies of the mother cells, and this can be repeated in a huge number of generations. Under the influence of radiation, the molecular structure of a chromosome or gene can change. As a result, a gene with new features is formed; it will no longer be an absolute similarity to the old one, i.e. mutation will occur.
A mutation is a change in a gene or chromosome. Before the next cell division, the altered chromosome reproduces a copy of itself, i.e. the changes that have occurred in it are transmitted to the chromosomes of subsequent generations of the cell. The mutated gene is inherited in this way; it becomes permanent. An organism that exhibits signs of a mutated gene is called a mutant. If the mutation occurred in the germ cell, then the developing organism will have new hereditary characteristics.
Distinguish gene, chromosomal and genomic mutations. Gene mutations are mutations resulting from a change in only one gene (they are also called point mutations). Chromosomal mutations are changes in the structure of chromosomes. All types of chromosomal mutations associated with a violation of the structure of chromosomes are called chromosomal aberrations (deviations). Genomic mutations, or karyotype mutations, are mutations associated with a change in the number of chromosomes.
As a result of mutations, dominant (dominant) and recessive (suppressed) genes can appear. If the gene is dominant, then the corresponding trait, the carrier of which it is, will be manifested in the offspring of the first generation, regardless of whether this gene is present in the germ cell of one or both parents. If the gene is recessive, then the corresponding trait carried by this gene, passing from generation to generation, can appear for the first time only in great-grandchildren, and then in the case when it is present in the germ cells of both the father and mother.
The appearance of mutations in somatic cells leads to the appearance of somatic effects of radiation. One of the manifestations of somatic mutations is malignant cell growth. Somatic cell mutations are not inherited. Mutations in somatic cells under the action of radiation lead to impaired immunogenesis. After irradiation, cells with chromosomal aberrations may appear in the lymphoid tissue, i.e. they are already mutants and can produce antibodies against normal host antigens.
Genetic consequences of exposure can be observed at any dose. The dose threshold below which radiation does not cause mutations has not been established.
Mutations lead to hereditary diseases. About 10% of newborns have certain hereditary disorders. Among autosomal dominant gene mutations, the following are known: aniridia, neurofibromatosis, muscular dystrophy, polycystic kidney disease, etc. Among autosomal recessive gene mutations, microcephaly, hydrocephalus, idiocy, ichthyosis, myopathy, hemophilia are most common. Mutations can lead to various malformations and deformities: heterochromia (different colors of the iris), heart defects, color blindness, polydactylism, "cleft lip", "cleft palate". Mutations can cause delayed physical and mental development. Some consider Down's disease to be a disease caused by radiation.
Gene mutations and chromosomal aberrations can lead to spontaneous miscarriages. If the psychology of children differs from normal ones due to hereditary defects, but they are born alive, the probability of surviving to a year is five times less than for healthy children.
Disability of the 2nd group from childhood pension Disability pension of the 2nd group in 2018 Assignment of any form of disability in Russia occurs solely on the basis of medical and social indicators. The assignment of disability category 2 is acceptable for people who are considered disabled, but do not need constant care. Such citizens are entitled to […]
