Organisms have similar hereditary variability. Variability: hereditary and non-hereditary. According to the level of occurrence
Hereditary, or genotypic variability - variability due to a change in the genotype; it happens: combinative- resulting from the recombination of hereditary material in the process of meiosis and the fusion of gametes; mutational leading to a change in the genetic material.
As a result of crossing over into prophase-1 of meiosis, into anaphase-1 of meiosis - as a result of divergence to the poles of haploid sets of chromosomes, in each of which the number of paternal and maternal sets can be different, and into anaphase-2, when chromatids diverge, differing as a result of crossing over. And when unique gametes merge, unique combinations of gene alleles in each genotype are formed, which fall under the control of selection.
mutational variability. The term "mutation" was first introduced into science by the Dutch geneticist G. de Vries. While experimenting with evening primrose (an ornamental plant), he accidentally discovered specimens that differ in a number of features from the rest (large growth, smooth, narrow and long leaves, red leaf veins and a wide red stripe on the calyx, etc.). Moreover, during seed propagation, plants from generation to generation steadfastly retained these characteristics. As a result of generalizing his observations, de Vries created a mutational theory, the main provisions of which have not lost their significance to this day: Mutations occur suddenly, abruptly, without any transitions; mutations are hereditary, i.e. persistently passed on from generation to generation; mutations do not form continuous series, they are not grouped around an average type (as with modification variability), they are qualitative changes. Mutations are not directed - any locus can mutate, causing changes in both minor and vital signs in any direction; the same mutations can occur repeatedly; mutations are individual, that is, they occur in individual individuals.
The process of occurrence of mutations is called mutagenesis, organisms in which mutations have occurred are called mutants, and environmental factors that cause the appearance of mutations are called mutagens. There are several classifications of mutations:
Mutations at the place of their occurrence: generative - arising in germ cells. They do not affect the characteristics of this organism, but appear only in the next generation. Somatic - arising in somatic cells. These mutations are manifested in this organism and are not transmitted to offspring during sexual reproduction (a black spot against the background of brown wool in astrakhan sheep). Somatic mutations can be saved only by asexual reproduction (primarily vegetative).
Mutations by adaptive value: beneficial - increasing the viability of individuals, more often harmful - decreasing, and neutral - not affecting the viability of individuals. This classification is very conditional, since one and the same mutation can be beneficial in some conditions, and harmful in others.
Mutations by the nature of manifestation: dominant - appear in the first generation and fall under the control of selection and recessive (mutations that do not appear in heterozygotes, therefore, remain in the population for a long time and form a reserve of hereditary variability). Most mutations are recessive.
Mutations by changing the state of the gene: direct - the transition of the gene from the wild type to a new state, reverse - the transition of the gene from the mutant state to the wild type. Mutations according to the nature of their appearance: spontaneous - mutations that arose naturally under the influence of environmental factors, induced - mutations artificially caused by the action of mutagenic factors.
Mutations according to the nature of the change in the genotype: gene, chromosomal, genomic. Mutations can cause various changes in the genotype, affecting individual genes, entire chromosomes, or the entire genome.
Genomic called mutations, as a result of which there is a change in the number of chromosomes in a cell. Genomic mutations arise as a result of a violation of mitosis or meiosis, leading either to uneven divergence of chromosomes to the poles of the cell, or to duplication of chromosomes, but without division of the cytoplasm. Depending on the nature of the change in the number of chromosomes, they distinguish: polyploidy - an increase in the number of chromosomes, a multiple of the genome. Polyploidy is more often observed in protozoa and in plants. Depending on the number of haploid sets of chromosomes contained in the cells, there are: triploids (3n), tetraploids (4n), etc. They can be: autopolyploids - polyploids resulting from the multiplication of genomes of the same species, allopolyploids - polyploids resulting from the multiplication of genomes different types(typical for interspecific hybrids).
heteroploidy (aneuploidy)- non-fold genome increase or decrease in the number of chromosomes. Most often, there is a decrease or increase in the number of chromosomes by one (less often two or more). Due to the non-disjunction of any pair of homologous chromosomes in meiosis, one of the resulting gametes contains one less chromosome, and the other one more. The fusion of such gametes with a normal haploid gamete at fertilization leads to the formation of a zygote with a smaller or a large number chromosomes compared to the diploid set characteristic of this species. Among aneuploids there are: trisomics - organisms with a set of chromosomes 2n + 1, monosomics - organisms with a set of chromosomes 2n -1. For example, Down's disease in humans occurs as a result of trisomy on the 21st pair of chromosomes.
Chromosomal mutations - mutations that cause changes in the structure of chromosomes. Rearrangements can be carried out both within the same chromosome - intrachromosomal mutations, and between non-homologous chromosomes - interchromosomal mutations.
Intrachromosomal mutations: deletion - loss of part of the chromosome (ABCD ® AB); inversion - rotation of a chromosome segment by 180˚ (ABCD ® ACBD); duplication - duplication of the same part of the chromosome; (ABCD® ABCBCD);
Interchromosomal mutations: translocation - transfer of a segment of one chromosome to another, non-homologous to it (ABCD ® ABCD1234). It is possible to combine two non-homologous chromosomes into one chromosome.
Gene mutations called changes in the structure of the DNA molecule in the region of a certain gene encoding the structure of a certain protein molecule. These mutations entail a change in the structure of proteins, that is, a new sequence of amino acids appears in the polypeptide chain, resulting in a change in the functional activity of the protein molecule.
Due to gene mutations, a series of multiple alleles the same gene. Often gene mutations occur as a result of the replacement of one or more nucleotides with others, insertion of nucleotides, loss of nucleotides, changes in the order of nucleotide alternation.
In nature, spontaneous mutagenesis is constantly going on. However, spontaneous mutations are rare. For example, in humans and other multicellular organisms, it is also 10 -5 per gene per gamete per generation. In other words, only in one of 100 thousand gametes the gene is changed. But there are a lot of genes in each gamete. According to modern estimates, the human genome contains about 30,000 genes. Consequently, in each generation, about a third of human gametes carry new mutations in some gene.
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.
Gene - a unit of storage, transmission and implementation 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 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. Variability is understood as the ability of organisms to acquire new features - differences within a 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 can 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. It may be the effect of certain chemical substances 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 great importance has, in particular, the age of the mother.
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 50% of the genes of the newly emerged organism 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 during 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 influence of the environment 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 the characteristics of nutrition, 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.
Think!
Questions
1. What chromosomes are called sex chromosomes?
2. What are autosomes?
3. What is homogametic and heterogametic sex?
4. When does genetic sex determination occur in humans and what causes it?
5. What mechanisms of sex determination do you know? Give examples.
6. Explain what sex-linked inheritance is.
7. How is color blindness inherited? What color perception will be in children whose mother is color blind, and whose father has normal vision?
Explain from the standpoint of genetics why there are many more color blind people among men than among women.
Variability- one of the most important properties of living things, the ability of living organisms to exist in various forms, to acquire new features and properties. There are two types of variability: non-hereditary(phenotypic, or modification) and hereditary(genotypic).
■ Non-hereditary (modification) variability. This type of variability is the process of the emergence of new traits under the influence of environmental factors that do not affect the genotype. Consequently, the resulting modifications of signs - modifications - are not inherited. Two identical (monozygous) twins, having exactly the same genotypes, but by the will of fate grown up in different conditions, can be very different from each other. A classic example proving the influence of the external environment on the development of traits is the arrowhead. This plant develops three types of leaves, depending on the growing conditions - in the air, in the water column or on the surface.
Under the influence of ambient temperature, the color of the coat of the Himalayan rabbit changes. The embryo, developing in the womb, is in conditions of elevated temperature, which destroys the enzyme necessary for dyeing wool, so rabbits are born completely white. Shortly after birth, certain protruding parts of the body (nose, tips of the ears and tail) begin to darken, because there the temperature is lower than in other places, and the enzyme is not destroyed. If you pluck an area of white wool and cool the skin, black wool will grow in this place.
Under similar environmental conditions in genetically close organisms, modification variability has a group character, for example, in summer, under the influence of UV rays, a protective pigment, melanin, is deposited in the skin of most people under the influence of UV rays, people sunbathe.
In the same species of organisms, under the influence of environmental conditions, the variability of various traits can be completely different. For example, in cattle, milk yield, weight, and fertility depend very strongly on the conditions of feeding and maintenance, and, for example, the fat content of milk under the influence of external conditions changes very little. Manifestations of modification variability for each trait are limited by their reaction rate. reaction rate- these are the limits in which a change in a trait is possible in a given genotype. In contrast to the modification variability itself, the reaction rate is inherited, and its boundaries are different for different traits and for individual individuals. The narrowest reaction rate is typical for signs that provide vital important qualities organism.
Due to the fact that most modifications have an adaptive value, they contribute to adaptation - the adaptation of the body within the limits of the norm of reaction to existence in changing conditions.
■ Hereditary (genotypic) variability. This type of variability is associated with changes in the genotype, and the traits acquired as a result of this are inherited by the next generations. There are two forms of genotypic variability: combinative and mutational.
Combination variability consists in the appearance of new traits as a result of the formation of other combinations of parental genes in the genotypes of offspring. This type of variability is based on the independent segregation of homologous chromosomes in the first meiotic division, the random meeting of gametes in the same parental pair during fertilization, and the random selection of parental pairs. It also leads to recombination of the genetic material and increases the variability of the exchange of sections of homologous chromosomes, which occurs in the first prophase of meiosis. Thus, in the process of combinative variability, the structure of genes and chromosomes does not change, however, new combinations of alleles lead to the formation of new genotypes and, as a result, to the appearance of offspring with new phenotypes.
Mutational variability It is expressed in the appearance of new qualities of the organism as a result of the formation of mutations. The term "mutation" was first introduced in 1901 by the Dutch botanist Hugo de Vries. According to modern ideas mutations are sudden natural or artificially induced inherited changes in the genetic material, leading to a change in certain phenotypic characteristics and properties of the organism. Mutations are undirected, that is, random, in nature and are the most important source of hereditary changes, without which the evolution of organisms is impossible. AT late XVIII in. in America, a sheep with shortened limbs was born, which gave rise to a new Ancon breed. in Sweden at the beginning of the 20th century. a mink with platinum fur was born on a fur farm. The huge variety of traits in dogs and cats is the result of mutational variation. Mutations arise abruptly, as new qualitative changes: awnless wheat was formed from spinous wheat, short wings and striped eyes appeared in Drosophila, white, brown, black color appeared in rabbits from the natural color of agouti as a result of mutations.
According to the place of origin, somatic and generative mutations are distinguished. Somatic mutations arise in the cells of the body and are not transmitted through sexual reproduction to the next generations. Examples of such mutations are age spots and skin warts. generative mutations appear in germ cells and are inherited.
According to the level of change in the genetic material, gene, chromosomal and genomic mutations are distinguished. Gene mutations cause changes in individual genes, disrupting the order of nucleotides in the DNA chain, which leads to the synthesis of an altered protein.
Chromosomal mutations affect a significant portion of the chromosome, leading to disruption of the functioning of many genes at once. A separate fragment of the chromosome can double or be lost, which causes serious disturbances in the functioning of the body, up to the death of the embryo in the early stages of development.
Genomic mutations lead to a change in the number of chromosomes as a result of violations of the divergence of chromosomes in the divisions of meiosis. The absence of a chromosome or the presence of an extra one leads to adverse consequences. The best-known example of a genomic mutation is Down syndrome, a developmental disorder that occurs when an extra chromosome 21 is added. In such people, the total number of chromosomes is 47.
In protozoa and in plants, an increase in the number of chromosomes, a multiple of the haploid set, is often observed. This change in the chromosome set is called polyploidy. The emergence of polyploids is associated, in particular, with the nondisjunction of homologous chromosomes during meiosis, as a result of which not haploid, but diploid gametes can form in diploid organisms.
Mutagenic factors. The ability to mutate is one of the properties of genes, so mutations can occur in all organisms. Some mutations are incompatible with life, and the embryo that received them dies in the womb, while others cause persistent changes in traits that are significant to varying degrees for the life of the individual. Under normal conditions, the mutation rate of an individual gene is extremely low (10 -5), but there are environmental factors that significantly increase this value, causing irreversible damage to the structure of genes and chromosomes. Factors whose impact on living organisms leads to an increase in the number of mutations are called mutagenic factors or mutagens.
All mutagenic factors can be divided into three groups.
Physical mutagens are all kinds ionizing radiation(y-rays, x-rays), ultraviolet radiation, high and low temperatures.
Chemical mutagens- these are analogs of nucleic acids, peroxides, salts of heavy metals (lead, mercury), nitrous acid and some other substances. Many of these compounds cause disturbances in DNA replication. Substances used in agriculture for pest and weed control (pesticides and herbicides), industrial waste, certain food colors and preservatives, some medications, components of tobacco smoke.
Special laboratories and institutes have been set up in Russia and other countries of the world to test all newly synthesized chemical compounds for mutagenicity.
Variation is the ability of organisms to acquire differences from other individuals of their species. There are three types - mutations, combinations and modifications.
MUTATIONAL VARIABILITY- these are changes in the DNA of the cell (changes in the structure and number of chromosomes). Occurs under the influence of ultraviolet radiation ( x-rays) etc. They are inherited, serve as material for (the mutation process is one of).
COMBINATIVE VARIABILITY occurs when the recombination (mixing) of the genes of the father and mother. Sources:
1) Crossing over during meiosis (homologous chromosomes closely approach and change areas).
2) Independent divergence of chromosomes during meiosis.
3) Random fusion of gametes during fertilization.
Example: the night beauty flower has a gene for the red color of the petals A, and the gene white color a. Organism Aa has pink petals, this trait occurs when a combination (combination) of the red and white gene.
MODIFICATION VARIABILITY occurs under the influence of the environment. It is not inherited, because with modifications only the phenotype (character) changes, and the genotype does not change.
Examples:
1) You can cut the dandelion root into 2 parts and plant them in different conditions; different-looking plants will grow, although they have the same genotype.
2) If a person is in the sun, he will tan; if he does physical education, he will increase his muscles.
3) When good content chickens increase egg production, cows give more milk.
Modification variability is not unlimited, for example, a white person can never tan to the state of a black man. The boundaries within which modification changes can occur are called "reaction rate", they are laid down in the genotype and are inherited.
MUTATIONS
Choose three options. Mutations lead to change
1) the primary structure of the protein
2) stages of fertilization
3) population gene pool
4) norms of reaction of a sign
5) sequences of phases of mitosis
6) the sex composition of the population
Answer
MUTATIONS ALL EXCEPT
1. Below is a list of characteristics of variability. All of them, except for two, are used to describe the characteristics of mutational variability. Find two characteristics that "drop out" of the general series, and write down the numbers under which they are indicated.
2) rotation of a chromosome segment by 180 degrees
3) decrease in the number of chromosomes in the karyotype
4) changes in the phenotype within the normal range of the reaction of the trait
5) gene recombination during crossing over
Answer
2. All but two of the characteristics below are used to describe mutational variability. Identify two characteristics that “fall out” of the general list, and write them down in the numbers under which they are indicated.
1) formed under the influence of x-rays
2) has a directed modification
3) changes within the normal range of reaction
4) is formed as a result of violation of meiosis
5) occurs suddenly in individual individuals
Answer
3. All but two of the characteristics below are used to describe mutational variability. Find two characteristics that "drop out" of the general series, and write down the numbers under which they are indicated.
1) depends on the action of radiation
2) can manifest itself with the loss of several nucleotides
3) is characterized by the appearance of an additional chromosome
4) depends on the breadth of the norm of the reaction of the trait
5) is determined by the combination of gametes during fertilization
Answer
4. All the processes below, except for two, are characteristic of mutational variability. Find two processes that "fall out" from the general list, and write down the numbers under which they are indicated.
1) a change in the trait within the normal range of the reaction
2) inheritance of autosomes
3) change in the number of chromosomes in a cell
4) loss of a chromosome segment
5) polyploidy
Answer
5. All of the characteristics below, except for two, are used to describe mutational variability. Find two characteristics that "fall out" from the general list, and write down the numbers under which they are indicated.
1) random combination of non-homologous chromosomes in meiosis
2) transfer of a chromosome segment to a non-homologous chromosome
3) decrease in the number of chromosomes in the karyotype
4) changes in the nucleotide sequence in the DNA structure
5) gene recombination during crossing over
Answer
6f. All but two of the following characteristics are used to describe mutational variability. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) an increase in the number of chromosomes in a cell
2) independent divergence of chromosomes in meiosis
3) conjugation and crossing over during reduction division
4) loss of a chromosome segment
5) change in the sequence of triplets in nucleic acid
Answer
MUTATIONS - COMBINATIONS
Establish a correspondence between the characteristic and the type of variability: 1) mutational, 2) combinative
A) occurs when exposed to radiation
B) is formed by the fusion of gametes
C) due to independent divergence of pairs of chromosomes
D) due to the exchange of genes between homologous chromosomes
D) is associated with an increase in the number of chromosomes in the karyotype
Answer
MUTATIONS - COMBINATIONS - MODIFICATIONS
Establish a correspondence between examples and types of variability: 1) combinative, 2) modification, 3) mutational. Write down the numbers 1-3 in the order corresponding to the letters.
A) the birth of a right-handed child from left-handed parents
B) a change in coat color in an ermine rabbit
C) the formation of green smooth and yellow wrinkled seeds in peas
D) the birth of a blue-eyed child from brown-eyed parents
E) the birth of smooth-haired offspring in guinea pigs with shaggy hair
E) the appearance of a flower with five petals at the lilac
Answer
COMBINATIONS ALL EXCEPT
1. Below is a list of characteristics of variability. All but two of them are used to describe the characteristics of combinative variability. Find two characteristics that “drop out” of the general series, and write down the numbers under which they are indicated in the table.
1) occurrence under the action of radiation
2) random combination of non-homologous chromosomes in meiosis
3) random combination of gametes during fertilization
5) change in the sequence of nucleotides in mRNA
Answer
2. The following characteristics, except for two, are used to describe the causes of combinative variability. Identify these two characteristics that “fall out” from the general list, write down the numbers under which they are indicated.
1) random meeting of gametes during fertilization
2) spiralization of chromosomes
3) DNA replication in interphase
4) recombination of genes during crossing over
5) independent divergence of chromosomes in meiosis
Answer
3. All of the characteristics below, except for two, are used to describe combinative variability. Find two characteristics that "fall out" from the general list, and write down the numbers under which they are indicated.
1) a random combination of non-homologous chromosomes in a gamete
2) change in the sequence of nucleotides in DNA
3) random meeting of gametes during fertilization
4) recombination of genes during crossing over
5) adequacy of phenotypic changes to environmental conditions
Answer
4. All of the characteristics below, except for two, are used to describe combinative variability. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) a combination of genes in the formation of gametes
2) the formation of the genotype during fertilization
3) the appearance in the offspring of combinations of traits that are absent in the parents
4) DNA change in the mitochondria of the egg
5) loss of amino acids and changes in protein structure
Answer
5. All the examples below, except for two, characterize combinative variability. Identify two examples that “fall out” from the general list, and write down the numbers under which they are indicated in the table.
1) a combination in the offspring of the characteristics of both parents
2) the appearance of a child with hemophilia in healthy parents
3) the appearance of a green body color in euglena in the light
4) the birth of a blue-eyed child from brown-eyed parents
5) darkening of the skin in humans when exposed to ultraviolet rays
Answer
COMBINATIONS - MODIFICATIONS
1. Establish a correspondence between the trait and the type of variability as a result of which it arises: 1) combinative, 2) modification
A) the appearance of a green body color in euglena in the light
B) a combination of parental genes
C) darkening of the skin in humans when exposed to ultraviolet rays
D) accumulation of subcutaneous fat in bears with excessive nutrition
E) the birth in the family of children with brown and blue eyes in a ratio of 1: 1
E) the appearance in healthy parents of children with hemophilia
Answer
2. Establish a correspondence between examples and forms of variability: 1) combinative, 2) modification. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) a change in the color of the coat of a white hare depending on temperature
B) the difference in weight in bulls of the same calving kept in different conditions
C) the appearance of wrinkled seeds in peas when crossing plants with smooth seeds
D) the presence of leaves of different lengths on one plant
D) the birth of a color-blind child in healthy parents
Answer
1. Analyze the table. For each lettered cell, select the appropriate term from the list provided.
1. somatic
2. non-hereditary
3. the birth of offspring with a new phenotype as a result of gene recombination due to crossing over
4. different body weight of bulls of the same offspring
5. mutational
6. hereditary
Answer
2. Analyze the table. For each lettered cell, select the appropriate term from the list provided.
1) somatic
2) hereditary
3) the birth of an individual with reduced wings in Drosophila parent organisms
4) different forms leaf blade of the arrowhead
5) mutational
6) non-hereditary
Answer
3. Analyze the table. For each lettered cell, select the appropriate term from the list provided.
1) modification
2) gene
3) a change in the color of the coat of a white hare depending on the time of year
4) hereditary
5) combinative
6) chromosomal
7) the birth of a wingless individual of Drosophila in winged parent organisms
8) non-hereditary
Answer
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) only genotype
2) genotype and phenotype
3) mutational
4) non-hereditary
5) phenotypic
6) the appearance of a flower with five petals at the lilac
7) the appearance of a thick undercoat in the fox in winter
8) the birth of a child with Down syndrome
Answer
Choose one, the most correct option. The reason for combinative variability may be
1) change in genes during DNA replication
2) chromosomal mutation
3) template DNA synthesis
4) random meeting of gametes during fertilization
Answer
Choose one, the most correct option. A change in the egg production of chickens within certain limits, depending on the conditions of detention, the feeding ration, is a manifestation
1) mutational variability
2) adaptation
3) norms of reaction of a sign
4) self-regulation
Answer
Pick two true statements and write down the numbers under which they are indicated in the table.
1) The form of hereditary variability due to a random combination of gametes is called combinative variability.
2) Phenotypic variability is associated with changes in the genotype.
3) Hereditary variability is associated with changes in the genotype.
4) Modification is a spontaneously occurring natural or artificially caused change in the genetic material.
Answer
Establish a correspondence between the characteristics of organisms and the ranges of their reaction rate: 1) narrow reaction rate, 2) wide reaction rate. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) body weight of cattle
B) the size of the human eyeball
C) the number of vertebrae in the cervical spine of mammals
D) the density of the wool of mammals
D) the size and shape of the plant flower
E) egg production of chickens
Answer
Choose one, the most correct option. An adaptive change in a particular trait within certain genetic limits is called
1) reaction rate
2) relative variability
3) mutation
4) combinative variability
Answer
Choose one, the most correct option. Sign reaction rate
1) is inherited
2) depends on the environment
3) is formed in ontogeny
4) depends on the number of chromosomes
Answer
© D.V. Pozdnyakov, 2009-2019
variability called common property all living organisms acquire differences between individuals of the same species.
Ch. Darwin singled out the following main types of variability: definite (group, non-hereditary, modification), indefinite (individual, hereditary, mutational) and combined. Hereditary variability includes such changes in the characteristics of living beings that are associated with changes in (i.e., mutations) and are transmitted from generation to generation. The transfer of material from parents to offspring must be very accurate, otherwise the species cannot be preserved. However, sometimes there are quantitative or qualitative changes in the DNA, and the daughter cells get distorted compared to the parental genes. Such errors in the hereditary material are passed on to the next generation and are called mutations. An organism that has received new properties as a result of mutations is called a mutant. Sometimes these changes are clearly visible phenotypically, for example, the absence of pigments in the skin and hair - albinism. But most often, mutations are recessive and appear in the phenotype only when they are present in the homozygous state. The existence of hereditary changes was known. All of it follows from the doctrine of hereditary changes. Hereditary variability is a necessary prerequisite for natural and. However, at the time of Darwin there were still no experimental data on heredity and the laws of inheritance were not known. This made it impossible to strictly distinguish between different forms of variability.
mutation theory was developed in the early twentieth century by the Dutch cytologist Hugo de Vries. have a number of properties:
Mutations occur suddenly, and any part of the genotype can mutate.
Mutations are more often recessive and less often dominant.
Mutations can be harmful, neutral or beneficial to the organism.
Mutations are passed down from generation to generation.
Mutations can take place under the influence of both external and internal influences.
Mutations are divided into several types:
Point (gene) mutations are changes in individual genes. This can happen when one or more nucleotide pairs in a DNA molecule are replaced, dropped or inserted.
Chromosomal mutations are changes in parts of a chromosome or whole chromosomes. Such mutations can occur as a result of deletion - loss of part of the chromosome, duplication - doubling of any part of the chromosome, inversion - rotation of the chromosome section by 1800, translocation - tearing off part of the chromosome and moving it to a new position, for example, attachment to another chromosome.
mutations consist in changing the number of chromosomes in the haploid set. This can occur due to the loss of a chromosome from the genotype, or, conversely, an increase in the number of copies of any chromosome in the haploid set from one to two or more. A special case of genomic mutations - polyploidy - an increase in the number of chromosomes by a factor. The concept of mutations was introduced into science by the Dutch botanist de Vries. In an aspen (primrose) plant, he observed the appearance of sharp, spasmodic deviations from the typical form, and these deviations turned out to be hereditary. Further studies on various objects - plants, animals, microorganisms showed that the phenomenon of mutational variability is characteristic of all organisms.
Chromosomes are the material basis of the genotype. Mutations are changes that occur in chromosomes under the influence of external factors or. Mutational variability is newly occurring changes in the genotype, while combinations are new combinations of parental genes in the zygote. Mutations affect various aspects of the structure and functions of the body. For example, in Drosophila, mutational changes in the shape of the wings (up to their complete disappearance), body color, development of bristles on the body, shape of the eyes, their color (red, yellow, white, cherry), as well as many physiological signs (lifespan, fertility) are known. ).
They take place in different directions and in themselves are not adaptive, beneficial changes for the body.
Many emerging mutations are unfavorable for the organism and can even cause its death. Most of these mutations are recessive.
Most mutants have reduced viability and are weeded out in the process. natural selection. Evolution or new breeds and varieties require those rare individuals that have favorable or neutral mutations. the significance of mutations lies in the fact that they create hereditary changes that are the material for natural selection in nature. Mutations are also necessary for individuals with new properties valuable to humans. Artificial mutagenic factors are widely used to obtain new breeds of animals, plant varieties and strains of microorganisms.
Combination variability also refers to hereditary forms of variability. It is due to the rearrangement of genes during the fusion of gametes and the formation of a zygote, i.e. during the sexual process.
