What is a mutation? This, contrary to misconceptions, is not always something scary or life-threatening. The term refers to a change in genetic material that occurs under the influence of external mutagens or the body’s own environment. Such changes can be useful, not affect the functions of internal systems, or, on the contrary, lead to serious pathologies.
Types of mutations
It is customary to divide mutations into genomic, chromosomal and gene mutations. Let's talk about them in more detail. Genomic mutations are changes in the structure of hereditary material that radically affect the genome. These include, first of all, an increase or decrease in the number of chromosomes. Genomic mutations are pathologies that are often found in the plant and animal world. Only three varieties have been found in humans.
Chromosomal mutations are persistent, abrupt changes. They are associated with the structure of the nucleoprotein unit. These include: deletion - loss of a section of a chromosome, translocation - movement of a group of genes from one chromosome to another, inversion - complete rotation of a small fragment. Gene mutations are the most common type of change in genetic material. It occurs much more often than chromosomal.
Beneficial and neutral mutations
Harmless mutations that occur in people include heterochromia (irises of different colors), transposition of internal organs, and abnormally high bone density. There are also useful modifications. For example, immunity to AIDS, malaria, tetrochromatic vision, hyposomnia (reduced need for sleep).
Consequences of genomic mutations
Genomic mutations are the causes of the most serious genetic pathologies. Due to changes in the number of chromosomes, the body cannot develop normally. Genomic mutations almost always lead to mental retardation. These include trisomy of chromosome 21 - the presence of three copies instead of the normal two. It is the cause of Down syndrome. Children with this disease experience learning difficulties and are delayed in mental and emotional development. The prospects for their full life depend, first of all, on the degree of mental retardation and the effectiveness of activities with the patient.
Another terrible deviation is monosomy of the X chromosome (the presence of one copy instead of two). Leads to another severe pathology - Shereshevsky-Turner syndrome. Only girls suffer from this disease. The main symptoms include short stature and sexual underdevelopment. A mild form of oligophrenia often occurs. Steroids and sex hormones are used for treatment. As you can see, genomic mutation is the cause of severe developmental pathologies.
Some chromosomal pathologies
Hereditary diseases caused by mutation of several genes at once or any violation of the chromosome structure are called chromosomal diseases. The most common of them is Angelman syndrome. This hereditary disease is caused by the absence of several genes on the 15th maternal chromosome. The disease manifests itself at an early age. The first signs are a decrease in appetite, absence or poverty of speech, and a constant smile for no reason. Children with this pathology experience difficulties with learning and communication. The type of inheritance of the disease is still being studied.
A disease similar to Angelman syndrome is Prader-Willi syndrome. Here, too, there is a lack of genes on the 15th chromosome, but not the maternal one, but the paternal one. Main symptoms: obesity, hypersomnia, strabismus, short stature, mental retardation. This disease is difficult to diagnose without genetic testing. As with many hereditary diseases, complete therapy has not been developed.
Some gene diseases
Gene diseases include metabolic disorders caused by a monogenic mutation. These are disorders of the metabolism of carbohydrates, proteins, lipids, and the synthesis of amino acids. A disease familiar to many, phenylketonuria, is caused by a mutation in one of many genes on the 12th chromosome. As a result of the change, one of the essential amino acids, phenylalanine, is not converted into tyrosine. Patients with this genetic disease must avoid any food containing even small amounts of phenylalanine.
One of the most serious connective tissue diseases, fibrodysplasia, is also caused by a monogenic mutation on chromosome 2. In patients, muscles and ligaments become ossified over time. The course of the disease is very severe. A complete treatment has not been developed. The type of inheritance is autosomal dominant. Another dangerous disease is Wilson's disease, a rare pathology that manifests itself as a disorder of copper metabolism. The disease is caused by a gene mutation on chromosome 13. The disease is manifested by the accumulation of copper in the nervous tissue, kidneys, liver, and cornea of the eyes. At the edges of the iris you can see the so-called Kayser-Fleischner rings - an important symptom in diagnosis. Usually the first sign of Wilson's syndrome is abnormal liver function, its pathological enlargement (hepatomegaly), cirrhosis.
As can be seen from these examples, gene mutation is often the cause of serious and currently incurable diseases.
MUTATION(lat. mutatio change, change) - a universal property of living organisms that underlies the evolution and selection of all forms of life and consists in a sudden change in genetic information. For medicine, the study of the nature of M. is extremely important from the point of view of the prevention and treatment of hereditary diseases (see).
The sudden onset of hereditary changes was described as early as the 18th and 19th centuries. This phenomenon was also known to Charles Darwin. However, the study of the phenomenon of M. began only after the formation of experimental genetics as a science at the beginning of the 20th century. The term “mutation” in the modern sense began to be used in scientific literature since 1901 after the publication of the book “Mutation Theory” by X. de Vries. Previously, the word “mutation” was used to describe individuals whose characteristics deviate from normal individuals.
After establishing the fact that genetic information is recorded in nucleic acid molecules, a radical change occurred in M.'s theory (see Gene, Deoxyribonucleic acids). Later it was found that heritable changes can occur not only in the DNA of chromosomes, but also in the DNA of cytoplasmic self-reproducing structures. In this case, they talk about cytoplasmic M.
The process of M.'s occurrence in natural conditions or as a result of experimental exposure to various physical and chemical conditions. and biol, factors are called mutagenesis (see).
An individual carrying M., the effect of the cut is manifested in the phenotype, is called a mutant. M. can change the external characteristics of an individual, its physical characteristics, biochemical processes, disrupt developmental processes, weaken viability (sublethal M.) or even lead to the death of the individual (lethal M.), etc. Along with M., the influence of -ry on the development of the individual is clearly expressed, there are M. that weakly change the normal development of the individual. Such M. are called small. M. can arise in germinal and somatic cells, in tissue culture cells, and, finally, in DNA molecules isolated from cells.
In terms of action, M. can be harmful, neutral, or beneficial, however, such an assessment is relative, since the effect of M. depends on environmental conditions. For example, for butterflies living on birch trees, M. melanism is harmful, because dark butterflies on light birch trunks are more easily detected by birds. However, in industrial areas, where tree trunks are darker, M. melanism has become useful.
Considering the importance of microorganisms for subsequent generations, they are divided into generative and somatic. Generative microorganisms arise in germ cells and pass into subsequent generations. Somatic M. are not transmitted to offspring. Appearing in a single cell of the body, they are inherited only by the descendants of this cell, forming mutant tissue in the body. Naturally, in the case of vegetative propagation, somatic microorganisms can persist for a long time. Somatic microorganisms are also widely known for animal organisms. In Drosophila, in the early stages of eye development, the normal allele (see Alleles) that determines the red color of the eyes can mutate in a separate cell into the allele that determines the white color of the eyes. The cell containing the newly appeared allele gives rise to tissue that occupies part of the eye, as a result of which, against a background of red color, a white sector appears in the eye of such a Drosophila (see Mosaicism). Somatic M., which arises at one or another stage of ontogenesis, genetically distinguishes the original cell and the tissue derived from it, which in some cases makes it possible to study the patterns of individual development. Somatic M. can have a serious impact on the life of an individual. The human body consists of approximately 10 14 cells. If we assume that a certain gene mutates with such a low frequency as 10 -8, then in this case the human body should contain more than 10 6 cells carrying M. only in this gene. The number of genes in a person is conditionally equal to 10 5. Even if we assume that the mutation frequency is extremely low (10 -8), we still get a huge number of mutant cells (10 11). This shows that a very large population of cells in the human body is influenced by M. Mutability, that is, the ability to change, is sharply increased in cancer cells. Apparently, in a number of cases the appearance of cancer is explained by somatic M. with subsequent tissue selection.
The successful development of research on the cultivation of human tissues has made it possible to determine the frequency of malignant genes in cells in direct experiments, as well as to study the genetic nature of malignant growth in experiments.
The characteristics inherent in a given species are developed in the process of evolution and are controlled by normal alleles, which are usually dominant in relation to the other gene of the allelic pair. It is obvious that the mutation process occurring in normal individuals mainly transforms dominant normal alleles into mutant recessive ones. However, the mutation process is reversible. Subsequent mutations in the mutant gene lead to the appearance not only of a series of other recessive alleles, but also to the appearance of normal dominant alleles. Changes from normal alleles to mutant ones are called direct mutations (A -> a), transformations of mutant recessive alleles into normal dominant ones are called reverse mutations (a -> A).
Under natural conditions, mutations appear under the influence of external and internal environmental factors and are designated by the term “natural (or spontaneous) mutations.” M. obtained under experimental conditions are called induced. The agents that cause M. are called mutagens (see). During the process of natural mutation, genes mutate at a certain frequency. The average frequency of M. per gene in one generation in bacteria is 10 -7, in Drosophila in germ cells - 10 -5, etc.
In the same organism, different genes mutate at different frequencies. Of the eight genes of the corn endosperm, the gene that controls color mutates with a frequency of 496 * 10 -6 , the Wx gene, which controls endosperm starchiness, mutates 330 times less often, with a frequency of only 1.5 * 10 -6 . The mutation frequencies of the remaining six genes represent the average value between the given extreme values.
Determining the frequency of M. in humans is much more difficult than in bacteria or plants. However, in some cases it is approximately established. Thus, the gene for intestinal polyposis mutates with a frequency of 10 -4, and the gene for progressive muscular dystrophy - with a frequency of 10 -5. The mutation frequency with direct M. (A -> a), as a rule, is higher than the mutation frequency with reverse M. (a -> A); the ratio of direct and reverse M. is characteristic of each individual gene. If we take into account the frequency of direct and reverse mutations in total for many genes, it becomes clear that the process of mutation is a massive, statistically well-fixed process.
In 1921, S. Wright proposed calling the stability of the mass mutation process the term “mutation pressure,” which characterizes the natural life of populations of organisms (see Population genetics). Direct and inverse movements are not necessarily a jump from one state only to another. Recessive and dominant alleles change in a variety of ways, as a result, many alleles arise from the same locus (see) in different organisms. The study of populations has shown that in some cases the number of alleles for individual genes amounts to tens and even hundreds. The W gene, localized on the X chromosome in Drosophila and determining eye color, has more than a dozen alleles, which control the eosin, honey, apricot, cherry, coral and white eye colors of fruit flies. The C + gene, which causes the appearance of gray coat color in a rabbit (agouti), mutates into three different recessive alleles: the C ch allele provides the chinchilla color of the rabbit, the C h allele provides white with black spots (Himalayan rabbit), and the c allele provides pure white.
Almost every gene, when tested by M., gives a series of multiple alleles. A classic example of a series of alleles is the alleles of blood group genes (see) in humans.
Antigen A appears in erythrocytes when people have the IA gene, antigen B appears when the IB gene is active. Both of these genes are allelic, their influence is independent of each other, they are not related to dominance or recessivity. This independent manifestation of alleles, when heterozygous individuals develop two traits under the influence of two alleles, is called codominance.
Multiple alleles participate in the creation of natural adaptive biol, characteristics of organisms.
When a mutation occurs in a separate gene, we talk about gene or point mutations. When there are changes in the structure of chromosomes (structural mutations, chromosome aberrations) or their number, we are talking about chromosomal mutations. The essence of chromosome aberrations is the dislocation of chromosome sections, i.e. their movement within a given chromosome or between different chromosomes. In the initial period of development of genetics, the presence of structural M. chromosomes was established by genetic analysis (see) and primitive observation of chromosomes. The possibility of fine observation of chromosomal mutations under a microscope appeared after the discovery of giant chromosomes in the salivary glands of Drosophila. In 1930, D. Kostov suggested, and T. S. Painter in 1933 proved that the structure of these chromosomes visible under a microscope, represented by a number of sequentially located disks, reflects their genetic content. Structural M. are widely represented in populations of plants, animals, and humans; on their basis, the evolution of species karyotypes is carried out (see). The main types of structural M. chromosomes are deletions (see), symmetric and asymmetric translocations (see), the formation of ring chromosomes (centric and acentric), duplications (see), inversions (see).
Translocations are the exchange of fragments between different chromosomes. This becomes possible when two breaks coincide - one in one chromosome and the other in the other. The resulting four fragments are freely combined with each other.
Divisions, i.e. loss of a section of a chromosome, can occur as a result of a single chromosome break. The terminal fragment, lacking a centromere, is lost. This type of deletion is called terminal. When two breaks appear, the middle section of the chromosome falls out, and the end fragments are combined into one chromosome. This is how interstitial deletions arise. The size of the deletions may vary. In cases where noticeable blocks of genes are lost, the zygotes die. Relatively small deletions are transmitted over generations through heterozygous individuals. However, when zygotes appear that are homozygous for the lost region, they usually die. M. caused by deletion in this case have a lethal effect.
A number of deletions have been discovered in humans that cause hereditary diseases. Thus, the terminal lack of part of the short arm of the 5th chromosome causes the appearance of the so-called. Cri Cat Syndrome, an interstitial deletion on chromosome 21 causes pernicious anemia.
The phenomena of duplication, i.e. doubling of any block of genes in chromosomes, can serve as a source of increasing the volume of genetic information of species; they are important from an evolutionary point of view.
The term “inversion” was introduced by A.H. Sturtevant in 1926 while studying crossing over in female Drosophila; he showed that the middle section of one of the chromosomes of the 3rd pair is turned over by 180°. Inversions can be single or complex, the latter leading to a noticeable rearrangement of gene blocks. If, during the formation of inversion, both breaks pass on the same side of the centromere, a paracentric inversion is formed. This inversion does not change the morphology of the chromosomes. However, in heterozygous individuals in the inverted region, crossing over does not occur for the block of genes contained in it (see Recombination). This ensures that the entire block is inherited. If the inversion involves the centromere, then a pericentric inversion occurs. When two inversions are directly adjacent to each other, so-called inversions appear. tandem inversions. This type of inversion has two forms: direct tandem inversion (with both inversions retaining the genes originally characteristic of their blocks in the chromosome) and reverse tandem inversion, when the gene blocks contained in the inversions change places. If there is one inversion, a second one can occur in its internal section. This type of chromosomal M. is called included inversion. If the second inversion occurs with partial capture of part of the material of the first inversion and part of the genes from the neighboring normal region of the chromosome, then it is called incoming. The reason for the absence of gene exchange in heterozygous individuals at the site of inversion is biol, the consequences of crossing over. In a heterozygous individual with a normal chromosome - 12345678 and a chromosome with inversion - 12654378, crossing over in section 5-6 will lead to the appearance of two crossing over chromosomes - 126678 and 123455437 8. In half of such chromosomes, some genes are lost, and in the other half, some genes are represented in double the amount. Such crossing-over effects are observed during paracentric and pericentric inversions. In the latter case, in addition, a chromatid with two centromeres (dicentrics) and a fragment without a centromere appear. The appearance of an unbalanced chromosome in the zygote leads to its death. The phenomenon when some of the zygotes in individuals regularly die, and the other part turns out to be normal, is called semi-sterility.
The phenomenon of translocation, which underlies another type of chromosomal M., consists of the transfer of a section of a chromosome to another chromosome or to another location on the same chromosome. In most cases, during translocations, chromosomes exchange sections. These translocations are called reciprocal, in contrast to non-reciprocal translocations, when the middle region of one chromosome is inserted into another chromosome. In this case, two breaks are required to form a middle fragment in one chromosome. The chromosome into which a foreign middle section is inserted breaks in one place. Mutual translocations are of two types: 1) symmetrical, arising from such an exchange of sections when one centromere is preserved in each chromosome (such translocations are associated with the preservation of all genetic material, which is distributed differently between chromosomes, they are passed on to subsequent generations); 2) asymmetric, observed during the fusion of two centromeric fragments and the formation of a dicentric chromosome. The connection of two acentric fragments leads to the appearance of one acentric fragment. During the replication (see) of chromosomes in the phase of DNA synthesis, the dicentric chromosome and the acentric fragment are doubled. In the first mitosis, acentric fragments are lost. As for the dicentric, it either forms a chromosome bridge and breaks, or, when both centromeres move to one pole, it enters the daughter cell. Through a series of mitoses, the dicentric is lost. Symmetrical translocations, due to the action of attractive forces of homologous loci in the prophase of meiosis (see), form a cruciform configuration. When diverging from such a figure, chromosomes often form a ring consisting of four chromosomes. Since symmetric translocations only accompany the redistribution of genetic material, individuals heterozygous for translocations, along with normal ones, produce gametes with abnormalities in the form of large duplications or deletions. Zygotes arising with the participation of such gametes die, which leads to semi-sterility of plants and animals heterozygous for mutual translocation. Translocations not only change the order of genes, but also the number of chromosomes due to the gain or loss of centromeres.
A unique type of structural chromosomes is the appearance of ring chromosomes. Normally, ring chromosomes are not found in the karyotype of animals and plants. The formation of a ring chromosome is associated with the occurrence of two breaks in one chromosome, resulting in the formation of two terminal and one middle fragment. The middle section is connected by places where there are breaks and is closed into a ring. If the middle section of the chromosome included a centromere, then a centric ring appears. Such a ring chromosome is passed on to generations of cells and organisms. If a ring chromosome is formed from the middle region of a chromosome lacking a centromere, an acentric ring chromosome arises.
There are two types of M. number of chromosomes: aneuploidy, that is, the loss or appearance of additional chromosomes (the M. unit is one or more chromosomes, the number of which is less than the haploid set); haploidy and polyploidy, a multiple change in the number of chromosomes, in which the unit of M is the haploid set of chromosomes (n). Haploidy is the loss of an entire set (2n - n). Polyploidy occurs when entire sets are added (2n + n, 2n + 2n, etc.). Individuals carrying three sets of chromosomes are called triploids (Zn), four sets are called tetraploids (4n), etc. Aneucloidies arise during mitosis or meiosis, usually due to nondisjunction of homologous chromosomes. The following types of aneuploidy are characteristic of diploids: nulisomy - loss of a pair of homologous chromosomes (2n - 2r, where r denotes homolog); monosomy - loss of one chromosome from any pair (2n - 1); trisomy - the appearance of one extra chromosome (2n + 1); tetrasomy - the presence of two extra homologous chromosomes (2n + 2r). With more complex phenomena, double monosomy (2n - 1 - 1), double trisomy (2n + 1 + 1), a combination of two types (2n - 1, 2n + 1), etc. are possible. Aneu-ploidy causes a violation of the gene balance and , as a rule, noticeably change the characteristics of an individual. Tetrasomy allows genes to be localized on specific chromosomes, since the presence of four chromosomes creates a system of three alleles in one of the parents, which changes the nature of segregation.
Aneuploidies in humans explain the emergence of a number of hereditary diseases. Aneuploidy in humans was first discovered by J. Lejeune et al. in 1959 when analyzing the chromosomes of a patient with Down's disease (see Down's disease). It turned out that the patients have trisomy on chromosome 21, which regularly occurs with a frequency of 1 in 700 births. With a frequency of 1 in 5000 eggs, due to nondisjunction of the X chromosomes, an egg is produced that lacks a sex chromosome (see Sex). Women with the XO genotype carry signs of Shereshevsky-Turner syndrome (see Turner syndrome). As a result of nondisjunction of X chromosomes, people appear with 47 chromosomes, including the XXY set. Children XXY turn out to be boys with the so-called. Klinefelter syndrome (see Klinefelter syndrome). Other aneuploid changes have been discovered in humans, in particular trisomy and tetrasomy on the X chromosome and combined trisomy. Complex disorders, the number of sex chromosomes, were found in men (XXXY, XXYY, XXXXY, XYY) and women (ХХХХ, ХХХХХ). Aneuploidy often occurs as somatic M. In the case of somatic M., aneuploidy as a result of nondisjunction of homologues in mitosis manifests itself as a chromosomal mosaic, in which some tissues have a normal set of chromosomes, while others consist of cells with an aneuploid number of chromosomes. In humans, chromosomal mosaics have been found along the sex chromosomes: XO/XX, XO/XY, XX/XY, XXY/XX хх/ххх, ххх/хо, хххх/ххххх, etc. (see Chromosomal diseases).
The term “haploidy” or “monoploidy” refers to the presence in the genome of only one homologue from each pair of chromosomes. In higher plants and animals, diploidity of chromosomes (pairing of alleles) contains one of the advantages of sexual reproduction and the viability of the organism during individual development, i.e., it is the most important genetic phenomenon.
Polyploidy is widely represented in plants. Polyploid plants differ from diploid ones in many morphological, physiological, and biochemical features. Their cells and nuclei are larger than those of diploids. The overall size of plants, their flowers, seeds and fruits are increased.
Polyploidy is less common in animals than in plants. This is due to the fact that for animals the gene balance between sex chromosomes and autosomes is of great importance. Deviation from diploidy in animals often causes sterility. Polyploid species are found among worms, insects, crustaceans, fish, amphibians, reptiles and other animals. Among these forms, some species have lost the ability to reproduce sexually. The connection between parthenogenesis and polyploidy has been established in crustaceans of the genus Artemia, woodlice Trichoni-seus, butterflies Solenobia, etc. Tetraploid forms that reproduce sexually are certain species of fish, the South American frog Odontophymis americanus and certain other organisms. Pacific salmon are polyploids, and the same applies to a number of carp fish species.
The cause is genetic, or so-called. point, M. is the replacement of one nitrogenous base in a DNA molecule with another, loss, insertion or rearrangement of nitrogenous bases in a DNA molecule. As a result of genetic M., a person may develop patol, conditions, the pathogenesis of which is different. The loss of one or more nucleotides (deletion) can lead to a violation of the sequence of amino acid residues in the polypeptide chain of the encoded protein, i.e., to a violation of its primary structure. Deletion of several nucleotides can lead to complete cessation of protein synthesis encoded by the mutant gene. A similar effect is possible in the case of transformation of a triplet encoding the inclusion of a certain amino acid in a polypeptide chain into a triplet encoding the end of the synthesis of the polypeptide chain.
Genetic M., without changing the amount of protein synthesized, can change its conformation and thereby its enzymatic activity up to its complete disappearance, and, conversely, without affecting the enzymatic activity of the protein, change the rate of its synthesis, the synthesis of its inhibitor or activator. All this ultimately leads to the development of enzymopathies (see).
All genetic diversity in people is, in one way or another, a consequence of M. The average frequency of occurrence of M per one human gamete turned out to be close to 1*10 -5. The frequency of the M. normal allele in the hemophilia allele (see) or in the albinism allele (see) is 3*10 -5. Human bone marrow cells in tissue culture mutate from the normal allele to the 8-azaguanine resistance allele with a frequency of 7*10 -4.
Enormous polymorphism in human populations exists not only due to individual genes, but also due to their combinations that create polymorphic systems of enzymes, blood groups, variability in tissue incompatibility alleles in the HLA locus, etc.
Bibliography: Auerbach S. Problems of mutagenesis, trans. from English, M., 1978; B a-r and shn e in Yu. I. and Velti-shch e in Yu. E. Hereditary metabolic diseases in children, JI., 1978; Berdyshev G. D. and Krivoruchko I. F. Human genetics with the basics of medical genetics, Kyiv, 1979; B about h-kov N. P. Human Genetics, M., 1978; Dubinin N.P. General, genetics, M., 1976; M a k u s i k V. A. Hereditary characteristics of a person, trans. from English, M., 1976; McKusick Y. Mendelian inheritance in man, Baltimore, 1978.
Please help me solve the problem and questions, I give all the points that I have. Problem: In some people, cells contain only one X chromosome (monosomics),but there are no people who have only a Y chromosome. Explain the reason for this phenomenon. Questions: 1) Describe the relationship between the concepts “gene”, “allele”, “crossing over”. 2) What is a mutation? When and where does mutation occur? You don't need to ask too many questions. In your own words. Thanks in advance to everyone who will help!)
1. What is reproduction? 2. What methods of reproduction are found in plants? 3. What type of reproduction is called sexual? 4. How does sexual reproduction occur?in Chlamydomonas? 5. How does spirogyra reproduce sexually? 6. How do mosses reproduce? 7. What conditions are necessary for the sexual reproduction of mosses? 8. Where do sperm develop in flowering plants? 9. What is a pollen tube? 10. Where is it located in flowering plants? egg? 11. How does double fertilization occur? 12. From what cell is the endosperm formed? 13. From what is the seed coat formed? 14. How is the seed embryo formed? 15.What is pollination?
help me please
sexual reproduction occurs in Chlamydomonas
5) how Spirogyra reproduces sexually
6) how mosses reproduce
7) what conditions are necessary for sexual reproduction of mosses
8) where sperm develop in flowering plants
9) what is a pollen tube
10) where the egg is located in flowering plants
11) how double fertilization occurs
12) from which cell is the endosperm formed?
13) what is the seed coat formed from?
14) how the seed embryo is formed
15) what is pollination
1. What is characteristic of a mutation (occurs during crossing, during crossing over, occurs suddenly in DNA or in chromosomes)?2. What signs of variability are transmitted to the offspring (modification, mutation)?
3. What changes when mutations occur (genotype, phenotype)?
4. Are genotype or phenotype traits inherited?
5. What variability is characterized by the following characteristics: occur suddenly, can be dominant or recessive, beneficial or harmful, inherited, repeated (mutational, modification)?
6. Where do mutations occur (in chromosomes, in DNA molecules, in one pair of nucleotides, in several nucleotides)?
7. In what case does the mutation manifest itself phenotypically (in any, in a homozygous organism, in a heterozygous organism)?
8. What is the role of mutations in the evolutionary process (increasing variability, adaptation to the environment, self-improvement of the organism)?
9. What does the phenotype depend on (the genotype, the environment, nothing else)?
10. What determines the scope of variability in an organism’s characteristics (environment, genotype)?
11. Signs of what variability are expressed in the form of a variation series and a variation curve (mutation, modification)?
12. Which signs have a narrow reaction rate (qualitative, quantitative), which are more flexible (qualitative, quantitative)?
13. Which form of natural selection in a population leads to the formation of new species (driving, stabilizing), which - to the preservation of species characteristics (driving, stabilizing)?
mutation) - a change in the amount or structure of DNA of a given organism. With a point mutation (or gene mutation), any one gene undergoes such a change; With a chromosomal mutation, the structure or number of chromosomes changes. All types of mutations are quite rare and can occur spontaneously or under the influence of any external agents (mutagens). If the mutation occurs in developing sex cells (gametes), it can be inherited. Mutations in any other cells (somatic mutations) are usually not inherited.
MUTATION
An abrupt change in genetic material caused by factors other than normal Mendelian recombination. Mutations become part of the genetic material (that is, they are genotypic), although their effect may not be evident in the phenotype of an individual organism. Most mutations affect individual genes, but there are also global chromosomal changes affecting many genes. A mutation can also occur in the cell body (called a somatic mutation), then it is transmitted through mitosis of that cell. In terms of the adaptive value of a mutation for an individual organism, the results are very random; their role in evolution is mediated by the process of natural selection. Generally speaking, large (macro) mutations are harmful to the organism, and therefore they are not passed on; small (micro) mutations, according to the standard point of view, are the very “essence” of evolution.
Mutation
sudden natural or artificially caused changes in the carriers of hereditary information of the body, not associated with the process of normal redistribution (recombination) of genes. The ability for M. is inherent in all plant and animal organisms and determines one of the two main forms of hereditary variability - mutational variability. There are three types of mutations: gene, chromosomal and genomic.
Mutation
lat. mutatio - change, change) is an abrupt and persistent change in genetic material caused by factors other than Mendelian gene recombinations considered normal. They are distinguished: 1. gametic mutations (occurring in generative, germ cells); 2. somatic mutations (occurring in somatic cells of the body). Depending on the nature of the changes in the genetic apparatus, mutations are further divided into: 3. genomic mutations (for example, diploidy, that is, doubling of the cell genome); 4. chromosomal mutations (for example, trisomy, that is, the appearance of one additional chromosome to the normal two); 5. gene mutations (for example, a change in the structure of one gene, several genes at the same time); 6. mutations of genes localized outside the cell nucleus are called cytoplasmic. Most known mutations affect individual genes; other mutations are less common. The role of mutations in evolution is mediated by the process of natural selection. The vast majority of mutations are destructive, disrupting the viability and preventing the evolution of biological species. See Darwinism.