Which organisms are called homozygous. Heterozygous and homozygous organisms

sign- a unit of morphological, physiological, biochemical, immunological, clinical and any other discreteness of organisms (cells), i.e. a separate quality or property by which they differ from each other.

The genotype is the genetic constitution of an organism, which is the totality of all the hereditary inclinations of its cells, contained in their chromosome set - the karyotype.

Genotype(from gene and type), the totality of all genes localized in the chromosomes of a given organism.

Phenotype (Phenotype) - the totality of all signs and properties inherent in the individual, which were formed in the process of his individual development.

Phenotype - a set of all the characteristics of an organism, formed in the interaction of the genotype with the environment.

Homozygosity, the state of the hereditary apparatus organism, in which homologous chromosomes have the same form of a given gene.

Heterozygosity inherent in every hybrid organism a condition in which its homologous chromosomes carry different forms (alleles) of a particular gene.

Hemizygosity(from Greek hemi- - semi- and zygotós - connected together), a condition associated with the fact that an organism has one or more genes that are not paired, that is, they do not have allelic partners. (In sex-linked inheritance, Xr or XR - r - daltonzyme)

35. Patterns of inheritance in monohybrid crossing.

monohybrid cross - crossing forms that differ from each other in one pair of alternative features.

1 Mendel's law: when crossing two homozygous organisms that differ from each other in one pair of alternative traits, uniformity in genotype and phenotype is observed in the first generation. (gingival fibromatosis - A, healthy gums- but the child is sick anyway)

2 Mendel's law: when crossing 2 heterozygous organisms that differ in one pair of alternative traits (F1 hybrids) in their offspring (F2 hybrids), splitting is observed according to the phenotype 3: 1, according to the genotype 1: 2: 1

Complete dominance is a phenomenon in which one of the allelic genes is predominant and manifests itself both in the heterozygous and in the homozygous state.

36. Dihybrid and polyhybrid crossing. The law of independent combination of genes and its cytological foundations. General formula splitting with independent inheritance.

Dihybrid crossing - crossing forms that differ in two pairs of studied characteristics

Polyhybrid cross - crossing forms that differ in many ways.

The law of independent inheritance of traits:

When crossing homozygous individuals that differ in two and large quantity pairs of alternative traits, in the second hybrid generation (with inbreeding of hybrids of the 1st generation), independent inheritance is fixed for each pair of traits and individuals appear with new combinations of traits that are not characteristic of parental and grandparental forms ( law of independent distribution, or Mendel's third law) (Brown eyes - B, blue eyes - b, right-handed - A, left-handed - a). Cleavage in relation to (3:1)n, and according to the phenotype 9:3:3:1. Task in the album.

Obviously, non-allelic genes located in different (non-homologous) chromosomes should obey this law first of all. In this case, the independent nature of the inheritance of traits is explained by the patterns of behavior not homologous chromosomes in meiosis. These chromosomes form with their homologues different pairs, or bivalents, which in metaphase I of meiosis randomly line up in the equatorial plane of the division spindle. Then, in anaphase I of meiosis, the homologues of each pair diverge to different poles of the spindle, independently of other pairs. As a result, each of the poles has random combinations of paternal and maternal chromosomes in the haploid set (see Fig. 3.75). Consequently, different gametes contain different combinations of paternal and maternal alleles of non-allelic genes.

The variety of types of gametes formed by an organism is determined by the degree of its heterozygosity and is expressed by the formula 2 n, where n- the number of loci in the heterozygous state. In this regard, diheterozygous F1 hybrids form four types of gametes with the same probability. The realization of all possible meetings of these gametes during fertilization leads to the appearance in F2 of four phenotypic groups of offspring in the ratio 9:3:3:1. Analysis of the F2 descendants for each pair of alternative traits separately reveals splitting in a ratio of 3:1.

37. Multiple alleles. Inheritance of human blood groups of the ABO system.

Multiple allelism - various states(three or more) of the same locus of chromosomes resulting from mutations.

The presence in the gene pool of a species of simultaneously different alleles of a gene is called multiple allelism. An example of this is the different eye color options in the fruit fly: white, cherry, red, apricot, eosin, due to different alleles of the corresponding gene. In humans, as in other representatives of the organic world, multiple allelism is characteristic of many genes. Thus, three alleles of gene I determine the blood group according to the AB0 system (IA, IB, I0). The gene that determines the Rh-belonging has two alleles. More than a hundred alleles account for the genes for α- and β-polypeptides of hemoglobin.

The cause of multiple allelism is random changes in the structure of the gene (mutations) that are stored in the process natural selection in the population's gene pool. The diversity of alleles that recombine during sexual reproduction determines the degree of genotypic diversity among representatives of a given species, which is of great evolutionary importance, increasing the viability of populations under changing conditions of their existence. In addition to evolutionary and ecological significance, the allelic state of genes has big influence on the functioning of the genetic material. In diploid somatic cells of eukaryotic organisms, most genes are represented by two alleles that together influence the formation of traits. tasks in the album.

38. Interaction of non-allelic genes: complementarity, epistasis, polymerism, modifying action.

Complementarity is a type of interaction when 2 non-allelic genes, falling into the genotype in a dominant state, jointly determine the appearance of a new trait that each of them does not individually determine. )

If one of the pair is present, it manifests itself.

An example is blood types in humans.

Complementarity can be dominant or recessive.

In order for a person to have normal hearing, it is necessary that many genes, both dominant and recessive, be coordinated to work. If at least one gene is homozygous for a recessive, hearing will be weakened.

Epistasis is the masking of the genes of one allelic pair by the genes of another.

Epistasis (from the Greek epi - over + stasis - obstacle) - the interaction of non-allelic genes, in which the suppression of the manifestation of one gene by the action of another, non-allelic gene is observed.

A gene that suppresses the phenotypic manifestations of another is called epistatic; a gene whose activity is changed or suppressed is called hypostatic.

This is due to the fact that enzymes catalyze different cell processes when several genes act on the same metabolic pathway. Their action must be coordinated in time.

Mechanism: if B turns off, it will mask the action of C

In some cases, the development of a trait in the presence of two non-allelic genes in the dominant state is considered as a complementary interaction, in others, the non-development of a trait determined by one of the genes in the absence of another gene in the dominant state is regarded as recessive epistasis; if a trait develops in the absence of a dominant allele of a non-allelic gene, and does not develop in its presence, they speak of dominant epistasis.

Polymeria is a phenomenon when different non-allelic genes can have an unambiguous effect on the same trait, enhancing its manifestation.

Inheritance of traits in the polymeric interaction of genes. In the case when a complex trait is determined by several pairs of genes in the genotype and their interaction is reduced to the accumulation of the effect of the action of certain alleles of these genes, in the offspring of heterozygotes varying degrees the severity of the trait, depending on the total dose of the corresponding alleles. For example, the degree of skin pigmentation in humans, determined by four pairs of genes, ranges from the most pronounced in homozygotes for dominant alleles in all four pairs (Р1Р1Р2Р2Р3Р3Р4Р4) to the minimum in homozygotes for recessive alleles (р1р1р2р2р3р3р4р4) (see Fig. 3.80). When two mulattos are married, heterozygous for all four pairs, which form 24 = 16 types of gametes each, offspring are obtained, 1/256 of which has the maximum skin pigmentation, 1/256 the minimum, and the rest are characterized by intermediate indicators of the expressivity of this trait. In the analyzed example, the dominant alleles of the polygenes determine pigment synthesis, while the recessive alleles practically do not provide this feature. The skin cells of organisms homozygous for the recessive alleles of all genes contain minimal amount pigment granules.

In some cases, dominant and recessive alleles of polygenes can provide development different options signs. For example, in the shepherd's purse plant, two genes have the same effect on determining the shape of the pod. Their dominant alleles form one, and recessive alleles form another form of pods. When two diheterozygotes are crossed for these genes (Fig. 6.16), a 15:1 split is observed in the offspring, where 15/16 offspring have from 1 to 4 dominant alleles, and 1/16 do not have dominant alleles in the genotype.

If the genes are located, each in its own separate locus, but their interaction manifests itself in the same direction, these are polygenes. One gene shows the trait slightly. Polygenes complement each other and have a powerful effect - a polygenic system arises - i.e. the system is the result of the action of identically directed genes. Genes are significantly influenced by the main genes, of which there are more than 50. Many polygenic systems are known.

At diabetes there is mental retardation.

Growth, intelligence level - determined by polygenic systems

modifying action. Modifier genes by themselves do not determine any trait, but can enhance or weaken the action of the main genes, thus causing a change in the phenotype. As an example, the inheritance of piebaldness in dogs and horses is usually given. Numerical splitting is never given, since the nature of inheritance is more reminiscent of polygenic inheritance of quantitative traits.

1919 Bridges coined the term modifier gene. Theoretically, any gene can interact with other genes, and therefore have a modifying effect, but some genes are modifiers to a greater extent. They often do not have their own trait, but are able to enhance or weaken the manifestation of a trait controlled by another gene. In the formation of a trait, in addition to the main genes, modifying genes also show their effect.

Brachydactyly - may be sharp or slight. In addition to the main gene, there is also a modifier that enhances the effect.

Coloration of mammals - white, black + modifiers.

39. Chromosomal theory of heredity. Linkage of genes. Clutch groups. Crossing over as a mechanism that determines gene linkage disorders.

Variability - the ability of living organisms to acquire new features and qualities. There are non-hereditary and hereditary variability (Scheme 1).

To non-hereditary variability include change change external signs(phenotype) that are not preserved in the generation. These include modifications that arise under the action environment.

in insects and other animals → change in coat color in some mammals when changing weather conditions(for example, in a hare) fig. 2,

in humans → an increase in the level of red blood cells when climbing mountains, an increase in skin pigmentation with intense exposure to ultraviolet rays, the development musculoskeletal system as a result of training (Fig. 3).

Rice. 3 Development of the musculoskeletal system as a result of training

hereditary variability represents changes in the genotype that persist over a number of generations. These include combinations and mutations. combination variability occurs when the recombination (mixing) of the genes of the father and mother.

Example: Drosophila manifestation with dark body and long wings when gray fruit flies with long wings are crossed with dark fruit flies with short wings (Fig. 4).

Rice. 4 Drosophila with dark body and long wings

the flower of the night beauty has petals Pink colour occur when a combination (combination) of the red and white gene (Fig. 5).

Rice. 5 The formation of pink petals in the night beauty

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.

in humans → trisomy of the 21st pair ( down syndrome),

in animals → double-headedness (Fig. 6).

Rice. 6 Two-headed turtle from China

GENOME

Genome - the totality of hereditary material located in the cell of the body. Most genomes, including the human genome and the genomes of all other cellular life forms, are built from DNA.

Deoxyribonucleic acid (DNA)- a macromolecule that provides storage, transmission and implementation from generation to generation of the genetic program for the development and functioning of living organisms.

Genotype is the totality of the genes of an organism.

So, the genome is a characteristic of the species as a whole, and the genotype is a separate individual.

Gene - the elementary unit of heredity of living organisms. A gene is a section of DNA responsible for the manifestation of a trait.

Genes there is in the core each cells living organism Fig. 7.

Rice. 7 Location of a gene in a cell

As a result of the interaction of the genotype with environmental factors, a phenotype , that is, the totality of all the signs and properties of an organism. Examples: height, body weight, eye color fig. eight, hair shape, blood type, left-handed, right-handed.

Rice. 8 Brown and blue eyes 9 Genotype and phenotype in peas

Tof e n about t and P at include not only external signs, but also internal ones: anatomical, physiological, biochemical. Each individual has its own characteristics of appearance, internal structure, the nature of metabolism, the functioning of organs, i.e. its phenotype, which was formed in certain conditions environment.

STRUCTURE OF THE CHROMOSOME

CHROMOSOMES are structural element nucleus, which contains all hereditary information (Fig. 10, 11, 12).

Rice. 10 Schematic representation of a chromosome

CENTROMERA The section of a chromosome that divides a chromosome into two arms.

Rice. 11 Image of a chromosome in an electron microscope

Rice. 12 The location of the chromosome in the cell

There are X-chromosome and Y-chromosome fig. 13.

X chromosome - sex chromosome most mammals, including humans, which determines the female sex of the organism.

Y chromosome - the sex chromosome of most mammals, including humans, which determines the male sex of the organism.

Females have two X chromosomes (XX), while males have one X chromosome and one Y chromosome (XY).

Rice. 13 X-chromosome and Y-chromosome

KARYOTYPE- a set of chromosomes characteristic of a given type of organism (chromosome set) Fig. fourteen.

Rice. 14 Karyotype healthy person

autosomes These are the same chromosomes for both sexes. Genotype female body has 44 chromosomes (22 pairs), the same as male. They are called autosomes. fourteen.

Rice. 15 Karyotypes of plants and animals

Rice. 16 Image of plants and animals of the corresponding karyotype:

skerda, butterfly, fruit fly, grasshopper and rooster

Karyotype- a set of external features of the chromosome set (number, shape, size of chromosomes) characteristic of a given species.

NITROGEN BASES

NITROGEN BASES- organic compounds included in the composition nucleic acids(DNA and RNA) fig. 17.

Latin and Russian codes for nucleic bases (nitrogenous base):

A - A: Adenine;

G - G: Guanine;

C - C: Cytosine;

T - T: Thymine, found in bacteriophages (bacterial viruses) in DNA, takes the place of uracil in RNA;

U - U: Uracil, found in RNA, takes the place of thymine in DNA.

Rice. 17 Nitrogenous bases in DNA and RNA

Rice. 18 Location nitrogenous bases in a cage

Nucleotide It is built from a pentose sugar, a nitrogenous base and a phosphoric acid (PA) residue.

hydrogen bond- this is the interaction between two electronegative atoms of one or different molecules through a hydrogen atom: G−Н ... C (line denotes covalent bond, three dots denote hydrogen bond) 19.

Rice. 19 Hydrogen bond

The principle of complementarity is used in DNA synthesis. This is a strict correspondence of the connection of nitrogenous bases connected by hydrogen bonds, in which: A-T (Adenine is connected to Thymine) G-C (Guanine is connected to Cytosine).

The principle of complementarity is also used in the synthesis of RNA, in which A-U (Adenine combines with Uracil) G-C (Guanine combines with Cytosine).

CROSSING

Crossbreeding - natural or artificial combination of two hereditarily different genotypes through fertilization.

Fertilization - the process of fusion of female and male germ cells (Fig. twenty.

Rice. 20 Fusion of egg and sperm

Gametes are the sex cells of animals and plants. Provides the transfer of traits from parents to offspring. It has a halved (haploid) set of chromosomes compared to a somatic cell. Sex cells that carry hereditary information.

Zygote- diploid (containing a complete double set of chromosomes) cell, resulting from the fertilization of fig. twenty

Rice. 21 Zygote

The emergence of a new organism as a result of fertilization, the fusion of male and female gamete with a haploid (single) set of chromosomes. biological significance: restoration of a diploid (double) set of chromosomes in the zygote (Fig. 21).

Rice. 22 Zygote - the result of fertilization

There are homozygotes and heterozygotes.

Homozygote- an organism (zygote) that has the same alleles of one gene in homologous chromosomes (AABB; AA).

heterozygote- an individual who gives different types gametes. heterozygote- the content in the cells of the body of different genes of a given allelic pair, for example Aa, arising from the combination of gametes with different alleles, for example AaBb, even for one AABb trait.

Dominance - the predominance of the effect of the action of a certain allele (gene) in the process of implementing the genotype in the phenotype, is expressed in the fact that the dominant allele more or less suppresses the actions of another allele (recessive), and the trait in question "submits" to it.

The dominant gene appears in both homozygous and heterozygous organisms.

The phenomenon of the predominance of the trait of parents in a hybrid is called dominance.

Rice. 23 Dominance of brown hair color and freckles

Rice. 24 Farsightedness Dominance

recessiveness- the absence of a phenotypic manifestation of one allele in a heterozygous individual (in an individual carrying two different alleles of the same gene). Suppressed (outwardly disappearing) sign.

Paired genes located on homologous chromosomes and controlling the development of the same trait are called allelic Fig. 25.

Rice. 25 Allelic genes

allelic genes- paired genes - various forms of the same gene responsible for the alternative (different) manifestation of the same trait. For example, two allelic genes located in the same loci (places) are responsible for eye color. Only one of them can be responsible for the development of brown eyes, and the other for the development of blue eyes. In the case when both genes are responsible for the same development of a trait, they speak of a homozygous organism for given feature. If allelic genes determine different development trait, they speak of a heterozygous organism. In species with a large number of individuals, at least 30-40% of the genes have two, three or more alleles. Such a stock of alleles provides a high adaptability of species to changing environmental conditions - this is the material for natural selection and at the same time a guarantee of the survival of the species. Genetic diversity within a species is determined by the number and distribution of alleles of different genes.

Crossing a homozygous organism with a recessive homozygote is called analyzing.

Analyzing cross - Crossing carried out to determine the genotype of an organism. To do this, the experimental organism is crossed with an organism that is a recessive homozygous for the trait under study. Suppose we need to find out the genotype of a pea plant that has yellow seeds. There are two variants of the genotype of the experimental plant: it can be either a heterozygote (Aa) or a dominant homozygote (Aa). To establish its genotype, we will carry out an analyzing cross with a recessive homozygote (aa) - a plant with green seeds.

Thus, if a splitting in the ratio of 1:1 is observed in F1 as a result of an analyzing cross, then the experimental organism was heterozygous; if no segregation is observed and all organisms in F1 show dominant traits, then the test organism was homozygous fig. 26.

Rice. 26 Analyzing crosses

Clean line is a group of genetically homogeneous (homozygous) organisms. Pure lines are formed only by homozygous plants; therefore, during self-pollination, they always reproduce one variant of the manifestation of the trait (Fig. 27. self pollination- pollination on one flower.

Rice. 27 Self-pollination

INCOMPLETE DOMINATION- one of the types of interaction of allelic genes, in which one of the alleles (dominant) in the heterozygote is not completely suppressed by the manifestation of another allele (recessive), and in the first generation the expression of the trait is intermediate (Fig. 28.

Rice. 28 Incomplete Dominance

The intermediate nature of the inheritance of the trait manifests itself with incomplete dominance.

Suppression by one dominant gene of the activity of another non-allelic dominant gene is called epistasis.

Rice. 28 Epistasis

Non-allelic genes are genes located in different parts of the chromosomes.

LAWS OF MENDEL

6.1 Mendel's first law - The law of uniformity of hybrids of the first generation.

The law of uniformity of hybrids of the first generation (Mendel's first law) - when crossing two homozygous organisms belonging to different pure lines and differing from each other in one pair of alternative manifestations of a trait, the entire first generation of hybrids (F1) will be uniform and will carry a manifestation of a trait of one of parents.

This law is also known as "the law of trait dominance". Its formulation is based on the concept clean line regarding the trait under study - on modern language this means that individuals are homozygous for this trait. When crossing pure lines of peas with purple flowers and peas with white flowers, Mendel noticed that the ascended descendants of plants were all with purple flowers, among them there was not a single white one.

Mendel repeated the experiment more than once, using other signs. If he crossed peas with yellow and green seeds, all the descendants had yellow rice seeds. 29.

Rice. 29 Crossing peas

If he crossed peas with smooth and wrinkled seeds, the offspring had smooth seeds. The offspring from tall and low plants were tall.

So, hybrids of the first generation are always uniform in this trait and acquire the trait of one of the parents. This sign is stronger, dominant (the term was introduced by Mendel from the Latin dominus), has always suppressed the other, recessive rice. thirty.

Rice. 30 First Law - The Law of Uniformity of Hybrids of the First Generation

6.2 Mendel's second law - splitting law.

The law of splitting, or the second law of Mendel. When two descendants of the first generation are crossed with each other (two heterozygous individuals), in the second generation F2, splitting is observed in a certain numerical ratio: according to the phenotype 3:1, according to the genotype 1:2:1. 25% of organisms obtained in the second generation F2 are homozygous dominant (AA), 50% are dominant (Aa) in phenotype and 25% are homozygous recessive (aa).

With incomplete dominance in the offspring of F2 hybrids, the splitting by phenotype and genotype is 1:2:1. The splitting law (Mendel's second law) - when two heterozygous descendants of the first generation are crossed with each other, in the second generation splitting is observed in a certain numerical ratio: according to the phenotype 3:1, according to the genotype 1:2:1.

The crossing of organisms of two pure lines that differ in the manifestations of one studied trait, for which the alleles of one gene are responsible, is called monohybrid crossing.

The phenomenon in which the crossing of heterozygous individuals leads to the formation of offspring, some of which carry dominant trait, and part is recessive, is called splitting. Therefore, splitting is the distribution of dominant and recessive traits among offspring in a certain numerical ratio. recessive trait in hybrids of the first generation does not disappear, but is only suppressed and manifests itself in the second hybrid generation Fig. 31, 32.

Rice. 31 Law of splitting

Rice. 32 Second Law

See also:

• HOMOYOTHERMAL ANIMALS(from the Greek homoios-equal, the same and therme- warmth), or warm-blooded (syn. homeothermic and homothermal animals), those animals that have a regulatory apparatus that allows them to maintain the t ° of the body approximately constant and almost independent ...
• HOMOLOGICAL SERIES, groups organic compounds with the same chem. function, but differing from each other in one or more methylene (CH2) groups. If in the simplest compound of a series of saturated hydrocarbons - methane, CH4, one of ...
• HOMOLOGUE ORGANS(from Greek ho-mologos-consonant, corresponding), the name of morphologically similar organs, i.e. bodies of the same origin, developing from the same rudiments and finding similar morfol. ratio. The term "homology" was introduced by the English anatomist R. Owen for ...
• HOMOPLASTY, or homoioplasty (from the Greek homoios-like), isoplasty, free transplantation of tissues or organs from one individual to another of the same species, including from one person to another. Start...
• HOMOSEXUALITY, unnatural sex drive to people of their own sex. G. was previously considered a purely psychopathological phenomenon (Krafft-Ebing), and psychiatrists and forensic doctors dealt with G.'s questions mainly. Only in recent times Thanks to the work...

Genetics- a science that studies genes, the mechanisms of inheritance of traits and the variability of organisms. During reproduction, a number of traits are passed on to offspring. It was noticed as early as the nineteenth century that living organisms inherit the characteristics of their parents. The first to describe these patterns was G. Mendel.

Heredity- the property of individual individuals to transmit their characteristics to offspring through reproduction (through sex and somatic cells). Thus, the characteristics of organisms are preserved in a number of generations. During the transfer of hereditary information, its exact copying does not occur, but variability is always present.

Variability- the acquisition by individuals of new properties or the loss of old ones. This is an important link in the process of evolution and adaptation of living beings. The fact that there are no identical individuals in the world is the merit of variability.

Inheritance of traits is carried out using elementary units of inheritance - genes. The totality of genes determines the genotype of an organism. Each gene carries encoded information and is located in certain place DNA.

Genes have a number of specific properties:

1. Different traits are encoded by different genes;
2. Persistence - in the absence of a mutating effect, the hereditary material is transmitted unchanged;
3. Lability - the ability to succumb to mutations;
4. Specificity - a gene carries specific information;
5. Pleiotropy - one gene encodes several traits;

Under the influence of environmental conditions, the genotype gives different phenotypes. The phenotype determines the degree of influence on the body of environmental conditions.

allelic genes

The cells of our body have a diploid set of chromosomes, they, in turn, consist of a pair of chromatids, divided into sections (genes). different forms identical genes (for example, brown / blue eyes), located in the same loci of homologous chromosomes, are called allelic genes. In diploid cells, genes are represented by two alleles, one from the father, the other from the mother.

Alleles are divided into dominant and recessive. The dominant allele will determine which trait will be expressed in the phenotype, and the recessive allele is inherited, but does not appear in a heterozygous organism.

Exist alleles with partial dominance, such a condition is called codominance, in which case both traits will appear in the phenotype. For example, they crossed flowers with red and white inflorescences, as a result, in the next generation they received red, pink and white flowers (pink inflorescences are a manifestation of codominance). All alleles are denoted by letters of the Latin alphabet: large - dominant (AA, BB), small - recessive (aa, bb).

Homozygotes and heterozygotes

Homozygote An organism in which alleles are represented only by dominant or recessive genes.

Homozygosity means having the same alleles on both chromosomes (AA, bb). In homozygous organisms, they code for the same traits (for example, White color rose petals), in which case all offspring will receive the same genotype and phenotypic manifestations.

heterozygote An organism in which alleles have both dominant and recessive genes.

Heterozygosity - the presence of different allelic genes in homologous regions of chromosomes (Aa, Bb). The phenotype in heterozygous organisms will always be the same and is determined by the dominant gene.

For example, A- Brown eyes, a - blue eyes, an individual with the Aa genotype will have brown eyes.

For heterozygous forms, splitting is characteristic, when, when crossing two heterozygous organisms in the first generation, we get next result: by phenotype 3:1, by genotype 1:2:1.

An example would be the inheritance of dark and light hair if both parents have dark hair. A - dominant allele on the basis of dark hair, and - recessive (light hair).

R: Aa x Aa

G: A, a, a, a

F: AA:2Aa:aa

*Where P - parents, G - gametes, F - offspring.

According to this scheme, you can see that the probability of inheriting a dominant trait (dark hair) from parents is three times higher than a recessive trait.

Diheterozygote- a heterozygous individual that carries two pairs of alternative traits. For example, Mendel's study of the inheritance of traits using pea seeds. The dominant features were yellow and smooth surface of seeds, and recessive - green color and rough surface. As a result of crossing, nine different genotypes and four phenotypes were obtained.

hemizygote- this is an organism with one allelic gene, even if it is recessive, it will always appear phenotypically. Normally, they are present on the sex chromosomes.

The difference between homozygotes and heterozygotes (table)

Reproduction, crossing of homozygotes and heterozygotes leads to the formation of new traits that are necessary for living organisms to adapt to changing environmental conditions. Their properties are necessary when breeding crops, breeds with high quality indicators.