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) - a set of all signs and properties inherent in an individual that 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, a state inherent in any hybrid organism in which its homologous chromosomes carry different shapes(alleles) of a particular gene.

Hemizygosity(from the 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 is color-tonzyme)

35. Regularities of inheritance in monohybrid crossing.

Monohybrid crossing - crossbreeding 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 in the first generation, there is uniformity in genotype and phenotype. (gum fibromatosis - A, healthy gums - a, the child is sick in any case)

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

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

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

Dihybrid crossing - crossing of forms differing in two pairs of studied traits

Polyhybrid crossing - crossing of forms that differ in many ways.

The law of independent inheritance of traits:

When crossing homozygous individuals that differ in two and big amount pairs of alternative traits, in the second hybrid generation (with inbreeding of 1st generation hybrids), independent inheritance is recorded for each pair of traits and individuals appear with new combinations of traits that are not characteristic of the parental and progenitor forms ( the law of independent distribution, or III Mendel's law) (Brown eyes - B, blue eyes - b, right-handed - A, left-handed - a). Cleavage in the ratio (3: 1) n, and the phenotype is 9: 3: 3: 1. The task in the album.

Obviously, this law should obey primarily non-allelic genes located in different (non-homologous) chromosomes. In this case, the independent character of the inheritance of traits is explained by the patterns of behavior of non-homologous chromosomes in meiosis. The named chromosomes with their homologues form different pairs, or bivalents, which, in metaphase I of meiosis, randomly line up in the plane of the fission spindle equator. 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, at each of the poles, random combinations of paternal and maternal chromosomes appear in a 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 the body is determined by the degree of its heterozygosity and is expressed by the formula 2 n, where n - the number of loci in a heterozygous state. In this regard, diheterozygous F1 hybrids form four types of gametes with the same probability. The realization of all possible encounters of these gametes during fertilization leads to the appearance in F2 of four phenotypic groups of offspring in a ratio of 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 - different states (three or more) of the same locus of chromosomes, resulting from mutations.

The presence in the gene pool of a species at the same time of different alleles of the gene is called multiple allelism. An example of this is the different color options for the eyes 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 inherent in many genes. Thus, three alleles of gene I determine the blood group according to the AB0 system (IA, IB, I0). Two alleles have a gene that determines Rh affiliation. More than one hundred alleles include the genes of α- and β-hemoglobin polypeptides.

Multiple allelism is caused by random changes in the structure of a gene (mutations) that are preserved in the process of natural selection in the gene pool of a population. The variety of alleles recombining 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 in the changing conditions of their existence. In addition to the evolutionary and ecological significance, the allelic state of genes has a great influence on the functioning of the genetic material. In diploid somatic cells of eukaryotic organisms, most genes are represented by two alleles, which together influence the formation of traits. Tasks in the album.

38. Interaction of non-allelic genes: complementarity, epistasis, polymerization, 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, which each of them does not determine individually. )

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

An example is human blood groups.

Complementarity can be dominant or recessive.

In order for a person to have normal hearing, many genes, both dominant and recessive, need to work, harmonize. If at least one gene is homozygous for recessive, hearing will be impaired.

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

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

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

This is because enzymes catalyze different processes cells, When several genes act on the same metabolic pathway. Their action must be coordinated in time.

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

In some cases, the development of a trait in the presence of two non-allelic genes in a dominant state is considered as a complementary interaction, in others, the lack of development of a trait determined by one of the genes in the absence of another gene in a dominant state is regarded as a 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 a dominant epistasis.

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

Inheritance of traits in 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, a different degree of severity of the trait is observed in the offspring of heterozygotes, 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 the dominant alleles in all four pairs (P1P1P2P2P3P3P4P4) to the minimum in homozygotes for recessive alleles (p1p1p2p2p3p3p4p4) When two mulattoes 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 expressiveness of this trait. In the analyzed example, the dominant alleles of the polygenes determine the synthesis of the pigment, while the recessive alleles practically do not provide this trait. The skin cells of organisms homozygous for the recessive alleles of all genes contain minimal amount pigment granules.

In some cases, dominant and recessive polygenic alleles can provide for the development of different options signs. For example, in a shepherd's purse plant, two genes have the same effect on determining the shape of the pod. Their dominant alleles form one, and recessive - another form of pods. When two diheterozygotes are crossed for these genes (Fig. 6.16), a splitting of 15: 1 is observed in the offspring, where 15/16 offspring have from 1 to 4 dominant alleles, and 1/16 has no dominant alleles in the genotype.

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

At diabetes mellitus mental retardation is observed.

Growth, level of intelligence - determined by polygenic systems

Modifying action. Modifier genes by themselves do not define any trait, but can enhance or weaken the action of the main genes, thus causing a change in the phenotype. An example is usually the inheritance of piebald in dogs and horses. Numerical splitting is never given, since the pattern of inheritance is more like polygenic inheritance of quantitative traits.

1919 Bridges coined the term gene modifier... In theory, any gene can interact with other genes, and hence exhibit a modifying effect, but some genes are modifiers to a greater extent. They often do not have a trait of their own, 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 action.

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

Mammal coloration - white, black + modifiers.

39. Chromosomal theory of heredity. Linking genes. Clutch groups. Crossing over as a mechanism determining gene linkage disorders.

nuclei, cells or multicellular organisms, copies of genes that are represented by different alleles in homologous chromosomes. When they say that a given organism heterozygous(or heterozygous for gene X), this means that the copies of genes (or a given gene) in each of the homologous chromosomes are slightly different from each other.

In heterozygous individuals, based on each of the alleles, slightly different variants of the protein (or transport or ribosomal RNA) encoded by this gene are synthesized. As a result, a mixture of these options appears in the body. If the effect of only one of them is externally manifested, then such an allele is called dominant, and the one whose effect does not receive external expression is called recessive. Traditionally, when schematically depicting a crossing, the dominant allele is denoted capital letter, and recessive is lowercase (for example, A and a); sometimes other designations are used, such as a gene abbreviation with plus and minus signs. Properly heterozygous are designated aA or Aa.

With complete dominance (as in Mendel's classic experiments with the inheritance of the pea shape), the heterozygous individual looks like a dominant homozygote. When homozygous plants with smooth peas (AA) are crossed with homozygous plants with wrinkled peas (aa), the heterozygous offspring (Aa) have smooth peas.

In case of incomplete dominance, an intermediate variant is observed (as in the inheritance of the color of the corolla of flowers in many plants). For example, when crossing homozygous red carnations (RR) with homozygous white carnations (rr) in heterozygous offspring (Rr), the corollas of flowers are pink.

If external manifestations are a mixture of the action of both alleles, as in the inheritance of blood groups in humans, then they speak of codominance.

It should be noted that the concepts of dominance and recessiveness were formulated within the framework of classical genetics, and their explanation from the standpoint of molecular genetics encounters certain terminological and conceptual difficulties.

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Homo is translated from Latin as the same, homozygous trait is a trait that is inherited in the body by the same gene, which is in a paired state (AA). Therefore, a homozygous organism is an organism in which a trait is inherited by the same gene.

The dominant feature is denoted by the letter A, the recessive feature is denoted by the letter a.

Hetero is translated from Latin as different, this is when in the body a trait can be inherited both by the dominant and by the recessive, i.e. there can be a trait inheritance like AA Aa and aa. In the first two cases, the trait is inherited by the dominant, and in the second case, by the recessive. Therefore, a heterozygous organism is an organism in which a trait is inherited by different genes.

• • Homozygous organism is an organism (animal or plant) that has two exactly the same genes, for example, two dominant genes for black (BB) or two recessive genes for brown (bb). For this reason, this organism is called pure.
  • Heterozygous organism is an organism containing one dominant and one recessive gene (for example, Bb). Such an organism is called hybrid.

In order to understand the World Cup in general, it is necessary to understand the genes, or rather, in their division into dominant and recessive ...

Dominant genes are those genes that dominate others, fight for your victory ...

Recessive genes are those genes that are suppressed and cannot fight with dominant ...

So homozygous organisms contain two dominant genes (from the word homo - the same) ...

Heterozygous organisms contain different genes, one dominant, the other recessive (from the word hetero - different) ...

So the fundamental difference is that genes can be either the same in vlvsti or different ...

The medical encyclopedia has a definition

Homozygous sex is a sex that has 2 identical sex chromosomes. In a homozygous (from the Greek homos means the same and zygote means paired) organism has 2 identical copies of a certain gene in homologous chromosomes.

Heterozygous sex is a sex that has different sex chromosomes or just one chromosome. In a heterozygous organism, also called a hybrid organism, by definition there are two different forms of a particular gene (different forms of a gene) in homologous chromosomes.

These are very complex definitions for those who have not come across such concepts, but the biological encyclopedia gives a very clear explanation, see the link here.

homo - homogeneous.

hetero - heterogeneous.

For organisms, this means that if the allelic genes are the same, then the organism is homozygous, and if different, then heterozygous, which can be used when crossing two organisms.

Homozygous and heterozygous organisms differ in the presence or absence of two identical genes. Have homozygous organisms or both are dominant or recessive (eg, dark hair and brown eyes). Have heterozygous one of the signs is dominant and the other is recessive (for example, blonde hair and brown eyes).

Homozygous (homo - the same) - those organisms in which two genes are equally dominant in the entire organism.

Hererozygous (hetero - different) - those organisms in which two genes are different, i.e. one is dominant and the other is depressed.

A homozygous (homos - the same, zygote - paired) organism with the same structures of this type. Both dominant or both recessive. And in heterozygous organisms, both traits are present - both dominant and recessive.

Homozygous organisms are organisms that have two genes identical in shape (either both dominant or both recessive);

Heterozygous organisms are organisms that have both dominant and recessive genes.

Homozygous organisms have no cleavage of traits, while heterozygous ones do.

There are dominant genes and recessive (weakly influencing) genes.

Dominant genes are capitalized English letter, for example A, and recessive - lowercase a.

In heterozygous organisms, usually one gene is dominant, and the second is recessive:

It is denoted like this: Aa.

When a given organism creates offspring, the dominant gene plays a decisive role in what the offspring will be, that is A.

For example, if we consider mice. If the dominant gene A is a fluffy coat, and recessive a- this is bald (there are bald albinos), then the dominant gene will win A and the descendant will be hairy. Moreover, this will still lead to an increase in the genus, since bald individuals are not protected from the cold and are likely to die, and the hairy ones will be able to live to grow up and leave offspring.

Homozygous organisms are organisms that have the same genes (alleles). Either two recessive aa, or two dominant AA.

Variability is the ability of living organisms to acquire new characteristics and qualities. Distinguish between non-hereditary and hereditary variability (Scheme 1).

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

in insects and other animals → change in coat color in some mammals when weather conditions change (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 ultraviolet rays, development of the 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 arises from the recombination (mixing) of the genes of the father and mother.

Example: the manifestation of fruit flies with a dark body and long wings when crossing gray fruit flies with long wings with dark fruit flies with short wings (Fig. 4).

Rice. 4 Drosophila with a dark body and long wings

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

Rice. 5 Formation of pink petals in a night beauty

Mutational variability- these are changes in the DNA of the cell (change in the structure and number of chromosomes). They arise under the influence of ultraviolet radiation, radiation (X-rays), etc.

in humans → trisomy for the 21st pair (Down syndrome),

in animals → biceps (Fig. 6).

Rice. 6 Two-headed turtle from China

GENOME

Genome - a set of hereditary material 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)- macromolecule providing storage, transmission and implementation from generation to generation of the genetic program for the development and functioning of living organisms.

Genotype- the set of genes of a given organism.

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

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

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

Rice. 7 Location of the gene in the cell

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

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

TOf e n O T and NS at include not only external signs, but also internal ones: anatomical, physiological, biochemical. Each individual has its own characteristics appearance, internal structure, the nature of metabolism, the functioning of organs, i.e. your phenotype, which was formed in certain conditions Wednesday.

STRUCTURE OF THE CHROMOSOME

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

Rice. 10 Schematic representation of a chromosome

CENTROMER - a section of a chromosome dividing a chromosome into two arms.

Rice. 11 Image of a chromosome in an electron microscope

Rice. 12 Location of the chromosome in the cell

There is an X chromosome and a Y chromosome fig. 13.

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

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

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

Rice. 13 X chromosome and Y chromosome

CARIOTYPE- a set of chromosomes characteristic of a given type of organisms (chromosome set) Fig. fourteen.

Rice. 14 Karyotype healthy person

Autosomes- these are the same chromosomes in both sexes. The genotype of the female organism has 44 chromosomes (22 pairs), the same as the male. They are called autosomes of rice. fourteen.

Rice. 15 Karyotypes of plants and animals

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

skerda, butterfly, fruit fly, grasshopper and rooster

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

NITROGEN BASES

NITROGEN BASES- organic compounds that make up 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 (bacteria 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 Nitrogen bases in DNA and RNA

Rice. 18 Location of nitrogenous bases in the cell

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

Hydrogen bond is the interaction between two electronegative atoms of one or different molecules through a hydrogen atom: G − H ... C (line indicates covalent bond, three dots - hydrogen bond) Fig. 19.

Rice. 19 Hydrogen bond

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

The principle of complementarity is also used in the synthesis of RNA, in which AU (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 spermatoroid

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

Zygote- a diploid (containing a complete double set of chromosomes) cell, formed as a result of fertilization of rice. twenty

Rice. 21 Zygote

The emergence of a new organism as a result of fertilization, the fusion of male and female gametes with a haploid (single) set of chromosomes. Biological significance: restoration of the 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) with the same alleles of one gene in homologous chromosomes (AABB; AA).

Heterozygote- an individual giving 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 connection of gametes with different alleles, for example AaBb, even for one AABb trait.

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

The dominant gene appears in both homozygous and heterozygous organisms.

The phenomenon of the predominance of the parent's trait in a hybrid is called dominance.

Rice. 23 Dominance of Riha hair and freckles

Rice. 24 Farsightedness dominance

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

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

Rice. Allelic genes

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

The crossing of a homozygous organism with a recessive homozygote is called analyzing.

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

Thus, if, as a result of the analyzing crossing in F1, a splitting is observed in a ratio of 1: 1, then the experimental organism was heterozygous; if no cleavage is observed and all organisms in F1 show dominant traits, then the experimental organism was homozygous to rice. 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 in 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 does not completely suppress the manifestation of the other 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 is manifested in 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 regions of chromosomes.

Mendel's Laws

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

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 the trait, the entire first generation of hybrids (F1) will be uniform and will carry the manifestation of the trait of one of parents.

This law is also known as the “law of dominance of traits”. Its formulation is based on the concept clean line with respect to 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 and used other signs. If he crossed peas with yellow and green seeds, all descendants had yellow rice seeds. 29.

Rice. 29 Crossing peas

If he crossed peas with smooth and wrinkled seeds, the offspring would have smooth seeds. Offspring from tall and low plants was high.

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

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

6.2 Mendel's second law - Splitting law.

Splitting law, or Mendel's second law. 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 for recessive trait (aa).

With incomplete dominance of F2 hybrids in the offspring, the phenotype and genotype segregation is 1: 2: 1. The law of splitting (Mendel's second law) - when two heterozygous offspring 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, differing 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 bears a dominant trait, and some are recessive, is called splitting. Therefore, splitting is the distribution of dominant and recessive traits among the offspring in a certain numerical ratio. The recessive trait in hybrids of the first generation does not disappear, but is only suppressed and manifests itself in the second hybrid generation. 31, 32.

Rice. 31 The law of splitting

Rice. 32 Second Law

There are several types and types of cells, differing in technology and functioning. Let's consider the main ones.

There are different points of view on project activities

The section is very easy to use. In the proposed field, just enter the desired word, and we will give you a list of its meanings. It should be noted that our site provides data from different sources- encyclopedic, explanatory, derivational dictionaries. Also here you can get acquainted with examples of the use of the word you entered.

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Heterozygote

heterozygote in the crossword dictionary

Dictionary of Medical Terms

heterozygote (hetero- + zygote)

a cell or organism that has different alleles for a given gene.

Encyclopedic Dictionary, 1998

heterozygote

HETEROSYGOTE (from hetero ... and zygote) a cell or organism in which homologous chromosomes carry different forms (alleles) of a particular gene. Wed Homozygote.

Heterozygote

(from hetero ... and zygote), a cell or organism that has different forms (alleles) of a particular gene in the hereditary set (genotype). G. is obtained by the fusion of gametes of different quality in terms of the genetic composition, each of which brings its alleles into the zygote. For example, homozygous AA and aa form gametes A and a, respectively. Obtained by crossing AA `aa G. always forms different-quality gametes: A and a. Crossbreeding of such a form within itself or with a recessive parental form aa gives offspring of two species - phenotypically A and phenotypically a (see Recessiveness, Phenotype). G. splitting occurs by a certain rule(see Mendel's laws). The preservation of G. is important for the agricultural sector. practice, because splitting often leads to the loss of valuable qualities. Almost all fruit trees heterozygous. To prevent them from splitting signs and loss of valuable properties, they resort to vegetative propagation or apomixis. Gynogenesis and parthenogenesis can also be used to maintain the heterozygous state. Wed Homozygote.

Yu.S. Demin.

Wikipedia

Heterozygote

Heterozygous called diploid or polyploid nuclei, cells or multicellular organisms, copies of genes that are represented by different alleles in homologous chromosomes. When they say that a given organism heterozygous(or heterozygous for gene X), this means that the copies of genes in each of the homologous chromosomes are slightly different from each other.

In heterozygous individuals, based on each of the alleles, slightly different variants of the protein (or transport or ribosomal RNA) encoded by this gene are synthesized. As a result, a mixture of these options appears in the body. If the effect of only one of them is externally manifested, then such an allele is called dominant, and the one whose effect does not receive external expression is called recessive. Traditionally, when schematically depicting a crossing, the dominant allele is denoted by a capital letter, and the recessive - by a lowercase (for example, A and a); sometimes other designations are used, such as a gene abbreviation with plus and minus signs. Properly heterozygous are designated aA or Aa.

With complete dominance (as in Mendel's classic experiments with the inheritance of the pea shape), the heterozygous individual looks like a dominant homozygote. When homozygous plants with smooth peas (AA) are crossed with homozygous plants with wrinkled peas (aa), the heterozygous offspring (Aa) have smooth peas.

In case of incomplete dominance, an intermediate variant is observed. For example, when crossing homozygous red carnations (RR) with homozygous white carnations (rr) in heterozygous offspring (Rr), the corollas of flowers are pink.

If external manifestations are a mixture of the action of both alleles, as in the inheritance of blood groups in humans, then they speak of codominance.

It should be noted that the concepts of dominance and recessiveness were formulated within the framework of classical genetics, and their explanation from the standpoint of molecular genetics encounters certain terminological and conceptual difficulties.

Examples of the use of the word heterozygote in the literature.

Expression of a recessive allele in the case of its hemizygous state or the presence of a deletion of a region with a dominant allele in heterozygotes.