What is incomplete dominance in biology definition. Inheritance with incomplete dominance

Observation between allelic genes; heterozygotes show signs intermediate in relation to parental. With incomplete dominance in the offspring of hybrids (F2), the splitting by genotype and phenotype coincides (1:2:1)

Example: coloring flowers of the night beauty.

Human genetic disease - brachydactyly - shortening of the middle phalanx of the fingers. The “b” gene is responsible for the development of the disease, a healthy person has the “BB” genotype. Patients with brachydactyly are heterozygotes and have the "BB" genotype. Homozygotes for the gene "vv" die before birth, that is, the gene "v" in the homozygous state is lethal.

codominance- independent expression of allelic genes. Each in the genotype shows its effect, and as a result, they show a new trait.

Example: the formation of the fourth blood group in humans. Inheritance of a blood group in humans according to the ABO system is due to gene I, there are 3 alleles of this gene. I O; I A; I B. Genes I A and I B are dominant in relation to I O, but co-dominant in relation to each other, and in persons with the genotype I A I B, 4 blood groups are manifested.

Complementarity b - manifestation of a sign of what is happening only if two dominant non-allelic genes are present in the genotype of the organism.

Example: complementary interaction of observations in the inheritance of crest shapes in chickens.

epistasis- the interaction of non-allelic genes, in which the gene of one allelic pair suppresses the action of another allelic pair. A gene that suppresses the action of another gene is called epistatic , suppressor or inhibitory. Epistasis can be dominant or recessive.

Example: dominant epistasis: inheritance of color determination in chickens. Dominant gene C - normal pigment production; c - does not provide enzyme synthesis; the dominant gene I of another allelic pair is a suppressor. As a result, chickens with genotype C and I turn out to be white.

Example: recessive epistasis is coat color in house mice

Polymerism- the phenomenon of simultaneous action on the trait of several non-allelic genes of the same type.

Example: inheritance of quantitative traits: color of wheat seeds, human skin, etc.; egg production, sugar content in sugar beets, etc.

Genes are responsible for the development of quantitative traits, have a cumulative effect, the more dominant genes, the brighter the trait.

Example: polymeric genes S 1 S 1 S 2 S 2 are responsible for human skin pigmentation. The more dominant genes in the genotype, the darker the skin.

Dark skin Light skin

P: S 1 S 1 S 2 S 2 x s 1 s 1 s 2 s 2

F1: S 1 s 1 S 2 s 2

From a marriage between mulattoes, children will be born with skin pigmentation from light to dark. The probability of having a child with black skin is 1/16.

VARIABILITY.

Variability- the ability of daughter organisms to differ from parental forms.

Variability

Non-hereditary Hereditary

(phenotypic, (genotypic,

modification, individual,

directional) random)

Combination Mutation

Modification variability (non-hereditary) - is an evolutionarily fixed adaptive response of the body to changes in environmental conditions without changing the genotype.

Characteristic - affects only the phenotype; not inherited; determined by the conditions of existence; is adaptive to environmental conditions.

Modification(from Latin "modificatio" - "modification") - a non-hereditary change in the phenotype that occurs under the influence of environmental factors within the normal range of the genotype reaction.

The limits within which a change in traits in a given genotype is possible is called reaction norm. According to the degree of variation of the reaction rate, signs are plastic and non-plastic. Plastic (broad reaction rate), examples: milk fat content in cows, human body weight, etc. Non-plastic (narrow reaction rate), examples are the color of the iris, the blood type of a person, etc.

Examples of modification variability:

The number of red blood cells in 1 ml 3 of blood almost doubles in climbers ascending to a height of 4000 m.

A pine tree grown on a mountain slope will be very different in growth and trunk shape from the same pine tree growing on a plain.

In people, individuality and talent are manifested as a result of the influence of genetic inclinations and the external environment, and the decisive role in this belongs to education and social relations.

Modification variability is characterized by the following features:

ü group nature of changes: for example, being under the influence of UV rays, all vacationers on the beach sunbathe, but the intensity of sunburn is different.

ü adequacy of changes: than more people exposed to the sun's rays, the more sunbathed.

ü the short duration of most modifications: people come from the south, and after a few weeks the tan disappears.

ü adaptability of changes: sunburn - protection of the body from the action of UV rays.

ü limitation: - the norm of the reaction.

Signs of the body can be:

Qualitative (eye and hair color in humans);

Quantitative (height and body weight in humans).

To characterize the degree of variability of quantitative traits, one of the statistical methods is used - the construction of a variation curve.

Darwin called the modification of changes definite, since. all individuals of the same species, having fallen into similar conditions, change in the same way, i.e., such variability is predictable, for example: all sheep, when grown in colder conditions, began to have thicker wool.

Genotypic called the variability of the genotype of the organism.

Feature: inherited; affects the genotype; is random in nature. It is divided into combinative and mutational.

combinative variability is associated with obtaining new combinations of genes present in the genotype. Due to: independent divergence of chromosomes in meiosis; random combination of chromosomes during fertilization; recombination of genes during crossing over.

Example: the appearance of green color of pea seeds when heterozygous plants are crossed with plants with yellow seeds.

Mutational variability- a change in the genotype itself, as a result of mutations.

Mutations- sudden abrupt and non-directional changes in DNA, with the appearance in living organisms of qualitatively new features and properties that did not previously exist in nature.

The main provisions of the mutation theory were developed by G. De Frisone.

Mutations occur suddenly, as discrete changes in traits;

New phenotypes are stable;

Unlike non-hereditary changes, mutations do not form continuous series representing qualitative changes;

Mutations can be harmful, neutral, or beneficial to the organism;

The probability of detecting mutations depends on the number of individuals studied;

Similar mutations can occur repeatedly.

The causes of mutations are the impact of mutational factors of various origins. They are divided into:

ü Physical (ionizing radiation: alpha, beta, gamma radiation, UV rays, heat);

ü Chemical (formalin, mustard gas, drugs, food preservatives, pesticides, etc.);

ü Biological (viruses, bacteria).

Gene mutations associated with a change in the DNA nucleotide sequence of one gene. Types of gene mutations manifest themselves in the following forms: duplications (repetition of a set of genes localized in this area), insertions, deletions (loss of chromosome sections in the middle part), inversions (rotation of the section by 180 o), defimensi (loss of end sections of chromosomes), translocation ( transfer of a segment to the other end of the same chromosome or to another non-homologous chromosome).

Example: defimensi - "cat's cry" syndrome - heterozygosity for defimensi in the fifth chromosome.

Chromosomal mutations associated with the movement of parts of chromosomes.

Genomics e mutations– change in the number of chromosomes in the cell genome (in the karyotype of an individual).

Genome- the content of hereditary material in the haploid set of chromosomes.

Genomic mutations include:

polyploidy(euploidy) - a multiple increase in the haploid set of chromosomes.

Cells with different numbers of haploid sets are called triploid (3), tetraploid (4), hexaploid (6), etc.

Polyploids are formed when the divergence of chromosomes to the poles of the cell is disturbed during mitosis. Polyploidy is found mainly in plants. Polyploid forms have larger leaves, flowers, fruits and seeds. Many cultivated plants are polyploids. There are 2 types of polyploidy: autopolyploidy and allopolyploidy.

heteroploidy(aneuploidy) - a type of genomic mutation in which there is a non-fold haploid increase or change in the number of chromosomes. (2n-1 - monosomy, 2n + 1 - trisomy; polysomy, etc.).

In humans, aneuploidy leads to infertility and often to chromosomal diseases (Down syndrome 2n = 47; Sherinevsky-Turner syndrome, Klinefelter syndrome, etc.).

Mutations are classified:

1) for the reasons that caused the mutation: spontaneous (under natural conditions) and induced (under the directed influence of mutation factors on the organs). These mutations were first obtained by G. A. Nadson and L. S. Filippov (1925) by irradiating fungi with radium, and by G. Meller (1927) by irradiating fruit flies with X-rays.

2) by the nature of the mutated cells: somatic - appear in the individual itself, are not inherited during sexual reproduction, are inherited during vegetative reproduction. Example: a different color of the iris in a person) and generative - occur in germ cells, are inherited, are detected phenotypically in descendants that are material for natural selection.

3) according to the outcome for the organism: negative - lethal / semi-lethal (decreased viability); neutral; positive (rare).

SELECTION

Breeding (from the Latin “selection” - “selection”, “choice”) is the production of new varieties of plants, animal breeds and strains of microorganisms with valuable properties for humans.

A breed, variety, strain is a population of organisms artificially created by man and characterized by certain hereditary characteristics.

The theoretical basis of selection is genetics.

The main selection methods are:

hybridization;

polyploidy;

mutagenesis;

cell and genetic engineering.

N. I. Vavilov - formulated the law homologous series in hereditary variability; the doctrine of finding material for selection is the idea he created of the centers of origin cultivated plants. He identified 7 such centers.

I. V. Michurin made a significant contribution to the selection of fruit crops. He performed the methods of hybridization, selection and exposure to environmental conditions ("mentor method") on developing hybrids. An important place in Michurin's breeding work was occupied by dominance control, which is based on the idea that under specific environmental conditions, hybrids develop predominantly traits that are favorable for these conditions.

INCOMPLETE DOMINATION

INCOMPLETE DOMINATION, in GENETICS - a situation in which no GENE is DOMINANT. As a result, the influence of both genes is observed in the body. For example, a plant with red and white flower genes can bloom pink.

Scientific and technical encyclopedic dictionary.

See what "INCOMPLETE DOMINATION" is in other dictionaries:

incomplete dominance- Intermediate manifestation of a trait in heterozygotes compared to those of dominant and recessive homozygotes. [Arefiev V.A., Lisovenko L.A. English Russian dictionary genetic terms 1995 407s.] Topics genetics EN semi… … Technical Translator's Handbook

Semi dominance, incomplete dominance Intermediate manifestation of a trait in heterozygotes compared to those of dominant and recessive homozygotes. (Source: "English-Russian Explanatory Dictionary of Genetic Terms". Arefiev ... Molecular biology and genetics. Dictionary.

incomplete dominance- nevisiškas vyravimas statusas T sritis augalininkystė apibrėžtis Vyravimo atvejis, kai F₁ hibride visu mastu nepasireiškia nei vienas iš tėvinių požymių. atitikmenys: engl. partial dominance; semi-dominance eng. incomplete dominance ryšiai:… … Žemės ūkio augalų selekcijos ir sėklininkystės terminų žodynas

dominance incomplete- * incomplete dominance or semi dominance ...

domination- interallelic interaction, manifested in complete (complete dominance) or incomplete (incomplete dominance) suppression by the dominant allele (A) of the action of the recessive allele (a) in the heterozygous state (Aa). With complete dominance ... ... Physical Anthropology. Illustrated explanatory dictionary.

See semi-dominance... Big Medical Dictionary

Dominance complete dominance p- Dominance is complete, dominance of n. D. p. in the strict sense is synonymous with the Mendelian concept of "dominance" (), ... ... Genetics. encyclopedic Dictionary

- (dominance) a form of relationship between the alleles of one gene, in which one of them (dominant) suppresses (masks) the manifestation of the other (recessive) and thus determines the manifestation of the trait both in dominant homozygotes and ... ... Wikipedia

Participation of only one allele in the determination of a trait in a heterozygous individual. The phenomenon of D. was discovered even in the first classic. G. Mendel's experiments. Dominant alleles represent capital letters A, B, etc. When there is no dominance in the strict sense of this ... ...

The patterns of distribution of inheritances and signs established by G. Mendel. The basis for the formulation of M. h. served as a long-term (1856 63) experiments on crossing several. pea varieties. G. Mendel's contemporaries could not appreciate the importance of ... ... Biological encyclopedic dictionary

Interaction of allelic genes or intraallelic interaction:

a) complete dominance- this is inheritance in which the dominant gene completely suppresses the recessive one, with this type of dominance, the dominant alleles (genes) show their effect both in the homozygous and in the heterozygous state, and the recessive alleles phenotypically appear only in the homozygous state.

Homo- and heterozygotes are indistinguishable;

b) incomplete dominance- this is inheritance in which the dominant gene does not completely suppress the recessive one, in this case the hybrids of the first generation have an intermediate trait, that is, there is an intermediate nature of inheritance, for example, inheritance of flower color in a night beauty, or blue plumage in chickens, coat color in large cattle, etc.

Homo- and heterozygotes differ from each other.

Not always signs can be clearly divided into dominant and recessive. In these cases, the dominant gene does not completely suppress the recessive gene from the allelic pair. In this case, intermediate signs will arise, and the sign in homozygous individuals will not be the same as in heterozygous ones. This phenomenon is called incomplete dominance. Let's explain it with an example.

When crossing plants of a night beauty with purple flowers (AA) with a plant with white flowers (aa), all plants of the first generation will have an intermediate pink color (Fig. 51). This does not contradict the rule of uniformity of hybrids of the first generation of G. Mendel: indeed, in the first generation, all the flowers are pink. When two individuals of the night beauty from the first generation are crossed, splitting occurs in the second generation, but not in a ratio of 3: 1, but in a ratio of 1: 2: 1, i.e. one flower is white (aa), two pink (Aa) and one purple (AA).

So far, we have considered the case of inheritance of one trait determined by one gene. But any organism has a huge number of signs, and these are not only external, visible features, but also biochemical signs (molecular structure, enzyme activity, concentration of substances in blood tissues, etc.), anatomical (size and shape of organs), etc. n. Any sign, no matter how simple it may seem, depends on numerous physiological and biochemical processes, each of which, in turn, depends on the activity of protein enzymes.

The totality of all external and internal signs and properties of an organism is called a phenotype.

The totality of all the genes of an organism is called the genotype.

Inheritance of flower color in a night beauty:

R: AA × aa

Red white

G: A a

F 1: Aa

Roz.

P (F 1): Aa × Aa

Roz. roses.

G: A a A a

F 2: AA Aa Aa aa

Kras. roses. roses. white

1. Purpose of the allowance

The manual is intended for use as a demonstration material in the 10th grade of the secondary secondary school in the course of general biology, in the lessons on the topic "Fundamentals of Genetics". The manual includes two sets: No. 1: "Incomplete dominance of the flower color gene when crossing a night beauty plant" and No. 2: "The manifestation of a new trait when two genes interact. The appearance of offspring with traits that are absent from the parents." The demonstration of the manual will allow students to get acquainted with the processes of crossing, different from the traditional monohybrid and dihybrid crossing, studied on the example of pea seeds (it is advisable to demonstrate these schemes in one lesson for comparison).

2. Set #1 INCOMPLETE DOMINATION

Description of the phenomenon

Incomplete dominance is a type of gene interaction in which an intermediate trait appears in the heterozygous state (Aa genotype). For example: the parents had red and white flowers, their genotypes were homozygous AA and aa. Hybrids of the first generation with the Aa genotype have pink flowers.

This type of interaction of allelic genes is often found in nature, including in humans. For example, the father's nose is large, and the mother's nose is small, the child's nose may be medium in size. Consider a specific example of the inheritance of flower color in a night beauty. Parental plants homozygous with the AA genotype have red flowers, and those with the aa genotype have white flowers. The AA and aa genes are located on homologous chromosomes in the first and second parent plants, respectively. In meiosis, homologous chromosomes merge together - conjugate, then diverge to different poles of the cell and end up in different gametes. The first plant forms gametes of the same type with gene A, the second plant also forms gametes of the same type, but these gametes contain gene a. Hybrids of the first generation F 1 are formed by the fusion of the gametes of the parents. From one parent comes the gene A, from the other - and, therefore, the genotype of Aa hybrids. The genes that determine the color of the flower are in a heterozygous state, plants show an intermediate sign - the flowers will be pink.

Let's consider which phenotypic classes and in what ratio will appear in F 2 . To obtain F 2 heterozygous F 1 plants are crossed with each other. During meiosis, each parent plant produces two types of gametes: half of the gametes will be with the A gene, and half will be with the a gene. In the process of fertilization, encounters of gametes with genes AA, Aa, Aa, aa are possible with equal probability. These genotypes correspond to phenotypes:

• AA - red flowers
• 2Aa - pink flowers
• aa - white flowers.

Thus, with incomplete dominance in F 2, three phenotypic classes are formed: red, pink, white in a ratio of 1:2:1.

Guidelines

1. Attach a card to the board with the letter "P", which means: "parents".
2. To the right and left of the "P" place cards of parents with alternative signs: on the left - red flowers, on the right - white. Pay attention to the genotype of the parents. They are homozygous, genotypes AA and aa. Between the cards of the parents under the letter "P" put the sign "X" (crossing).
3. 3. The gametes of each parent participate in the process of crossing. According to the scheme, attach the "gamete" card. Cards with gametes of each parent are attached below: on the left - A, on the right - a. Between them, but below, card F 1 is attached. Cards with pink flowers and heterozygous Aa genotypes are added to the right and left of it. Attention is focused on the fact that an intermediate sign is manifested, which is typical for incomplete dominance.
4. Let's consider with what signs and in what ratio there will be individuals in F 2. Attach the card "F 2" to the left of the collected application, then the crossing sign "X" under the sign "F 1" between the genotypes of heterozygotes: Aa X Aa. The "gametes" card is attached below, cards with gametes A and a for one parent (left) are fixed under it, and exactly the same - on the right, under the genotype of the second parent.
5. Two types of gametes of one parent and two types of gametes of the other parent give 4 types of possible combinations: AA - red flowers (the corresponding card is attached), Aa - pink flowers (the card with pink flowers is attached). It is noted that such a combination is possible twice: A - from the left parent, and - from the right. It is possible vice versa: a - from the left, A - from the right. The card "pink flowers" is attached a second time. And finally, the combination aa - white flowers. A card with white flowers is attached.

It turned out three classes of plants by phenotype: white, pink and red flowers. The ratio between the classes is 1:2:1. This splitting in F 2 is characteristic of incomplete dominance.

1. What genes are called allelic?
2. What types of interaction of allelic genes do you know?
3. How many phenotypic classes are in "F 1" with complete and incomplete dominance?
4. How many phenotypic classes are in "F 2" with complete and incomplete dominance?
5. What are the relationships between classes in "F 2" with complete and incomplete dominance?

3. Set No. 2 The emergence of new features in the interaction of two pairs of genes. The appearance of offspring with traits that are absent from the parents.

Process description

The development of genetics at the beginning of the 20th century showed that the manifestation of one trait is not always determined by a pair of allelic genes AA, Aa or aa.

Rabbit coat color is determined by two pairs of genes. The gray coat color is encoded by the dominant gene A, the black color is encoded by the recessive gene - a. Then gray rabbits can have the genotype AA or Aa, black rabbits - only the recessive genotype aa. However, the work of these genes is influenced by other genes C and c. Each individual can have the CC, Cs or ss genotype. If an individual has a dominant allele C, that is, its genotype is CC or Cs, then the color of the rabbit will be gray (genotypes AA or Aa) or black (genotype - aa). In the event that a combination of recessive allelic cc genes is present in the rabbit genotype, then the work of the A and a genes is suppressed, the pigment is not synthesized, and the rabbits will be white.

This type of interaction of non-allelic genes, in which some genes suppress the work of other non-allelic genes, is called epistasis.

The trait of coat color in a rabbit is controlled by two pairs of genes; gametes are formed as in a dihybrid cross. The Punnett lattice is filled in the same way as in a dihybrid cross, and the splitting in "F 2" will not be 9:3:3:1, but different. In "F 2" a trait may appear that was not in the parents and hybrids "F 1".

A specific example should be considered: the inheritance of coloration in rabbits.

Guidelines

1. Write out the letter designations of genes on the board in the corner. Coat color genes: A - gray color, a - black color. Genes that control the work of color genes: CC, CC - color appears, cc - color is suppressed.
2. Attach the "P" card to the board - parents. To her left is a card with a gray rabbit, its genotype is AACC. He is homozygous for gene A and gene C. AA - gray coat color, CC - pigment is formed. To the right of the "P" card is attached a card with a white rabbit with the genotype - aass, aa - the pigment is black, but the cc genes prohibit the synthesis of this pigment, and the rabbit will be white. Between these two cards, a crossing sign "X" is placed.
3. The cross involves the gametes of both parents. Attach a gamete card. Cards with the corresponding gametes are attached under it. Gray rabbit gametes AS, white rabbit gametes - ac. In "F 1 " hybrids are formed due to the fusion of parental gametes AaCs. These rabbits will be gray because they have gene A (gray color) and gene C (pigment is synthesized). F1 hybrids are heterozygous for two genes.
4. Below the gametes, a card "F 1" is attached, to the left and right of which cards with gray heterozygous rabbits (genotypes - AaCC) are placed.
5. To obtain F 2 hybrids F 1 are crossed with each other. Between the hybrid gray rabbits, an "X" card (crossing) is placed, and below the "gametes" card. Under it, the gametes of one parent are attached horizontally, and the other - vertically, that is, the boundaries of the Punnett lattice are depicted. Each parent has 4 types of gametes due to possible combinations of two pairs of genes:

Thus, a split into three phenotypic classes was obtained: rabbits are gray, black and white in a ratio of 9:3:4. The trait "black color" appeared, which neither the parents nor the F 1 hybrids had.

4. Storage rules

Keep the manual in a dry, heated room.

AT In nature, along with complete dominance, incomplete (intermediate) often occurs, when heterozygotes have a different phenotype than the original parental forms, the expression of the trait in the heterozygote is intermediate. Incomplete dominance is the weakening of the action of the dominant allele in the presence of a recessive one.

For example, in humans, anophthalmia (lack of eyeballs) is due to an autosomal recessive gene, the normal size of the eyeballs is due to a dominant gene. Heterozygotes have microphthalmia, i.e. reduced size of the eyeballs. In homozygotes for recessive alleles, eyeballs are absent, in heterozygotes, microphthalmia is found, in homozygotes for dominant alleles, apples have a normal size. A task 3

To determine the genotype and phenotype of the offspring of children by the phenotype and genotype of the parents with incomplete (intermediate) dominance

A healthy woman with normal eyeball size marries a man with anophthalmia (lack of eyeballs). What is the prognosis of the offspring if the children from the specified couple marry their own kind (selected marriages).

Solution:

Let's name the genes determining the development of the eyeballs: A- normal value eyeballs, a - anophthalmia, Aa - microphthalmia

F 2: AA: 2Aa: aa

1:2:1 three phenotypic classes, splitting by phenotype.

1:2:1 three genotypic classes, splitting by genotype. Answer:in the first generation (F1) when parents are homozygous (anophthalmia appears only in homozygotes for recessive alleles), all children have a reduced size of apples (microphthalmia); genotypically they are all heterozygous, i.e. manifested I law (rule) of uniformity. G. Mendel, however, phenotypically, children do not resemble their parents.

In the second generation (F 2) with incomplete dominance, the splitting by phenotype and genotype coincides 1:2:1, those. 1/4 (25%) of children with a normal size of the eyeballs; 1/2 (50%) with microphthalmia 1/4 (25%) of children with no eyeballs (anophthalmia).

In humans, the sign of wavy hair is inherited by incomplete dominance, diseases: acatalasia, microphthalmia, phenylketonuria, sickle cell anemia, etc. Deviations from expected segregation associated with lethal genes

In nature, in some cases, in the second generation, splitting may differ from what is expected, due to the fact that homozygotes for some genes are not viable. In humans, the dominant brachydactyly gene is similarly inherited (shortened phalanges of the fingers and a reduced number of phalanges themselves). In marriages, when a husband and wife suffer from brachydactyls, children are born in the ratio: two parts short-toed and one part with normal fingers (2:1, not 3:1), dominant homozygous individuals die while still in embryonic development.

Task 4

To determine the phenotype and genotype of offspring by phenotype and genotype

parents when deviating from expected splitting

One of the breeds of chickens is distinguished by shortened legs. This feature is dominant. The gene controlling it also causes shortening of the beak at the same time. At the same time, in homozygous chickens, the beak is so small that they are not able to break through the egg shell and die without hatching from the egg. In the incubator of the farm, which bred only short-legged hens, 4,500 chickens were obtained. How many of them are short-legged?

Solution:

Let us denote the genes that determine the development of the legs and beak.

A - shortened beak and shortened legs

a- normal beak,

AA - shortened beak, shortened legs, lethal homozygotes.

Since only short-legged chickens were bred in the incubator, therefore, all chickens in this farm are heterozygous by genotype (homozygotes, as noted, die without hatching).