Genotype- This is a set of genes received by the body from its parents.

Phenotype - This is the totality of all the properties and characteristics of an organism that develop on the basis of the genotype under certain environmental conditions.

A separate feature is called hairdryer(eye color, nose shape, stomach volume, red blood cell count, etc.).

The basic patterns of inheritance were studied by G. Mendel. They are inherent in all living organisms.

To explain the patterns of inheritance established by Mendel, it is proposed gamete purity hypothesis (Batson, 1902): in a hybrid organism, genes do not hybridize (do not mix) and are in a pure allelic state; during meiosis, homologous chromosomes separate and only one gene from the pair enters the gamete allelic genes.

Chapter 1. Patterns of gamete formation, basic theoretical principles

Gametes (sex cells) - contain a haploid set of chromosomes and are formed in the gonads (eggs - in the ovaries, sperm - in the testes) during the process of meiosis.

When prescribing gametes, you need to know that:

during meiosis, from each pair of homologous chromosomes one chromosome enters the future gamete, therefore, from each pair of allelic genes - one gene;

if the organism is homozygous (for example, AA), then all gametes, no matter how many of them are formed, will contain only one gene ( A), i.e. they will all be of the same type and, therefore, a homozygous organism forms one type of gametes;

if the organism is heterozygous ( Ahh), then in the process of meiosis one chromosome with the gene A gets into one gamete, and the second homologous chromosome with the gene A will fall into another gamete, therefore, a heterozygous organism for one pair of genes will form two types of gametes;

formula for prescribing gametes N = 2 n , Where N is the number of gamete types, and n - is the number of characteristics by which a given organism heterozygous.

Solving Typical Problems

Task 1. The nucleus of a human somatic (non-reproductive) cell contains 23 pairs of chromosomes. What is the possible diversity of gametes of one individual, if crossing over is not taken into account?

Solution . From each homologous pair of chromosomes, one gets into the gamete. Selecting a chromosome from the first pair gives two possibilities; the addition of a chromosome from the second pair doubles the number of variants, from the third pair - twice more, etc. In total we have 222......... 2 = 2 23 = 8  10 6 gamete options.

Task 2. Write down the types of gametes that are formed in individuals with genotypes:

A) AA;

G) AaBb.

Solution . According to the formula N=2 n we determine the number of gamete types in individuals of the following genotypes: in an individual AA - 1 type of gametes (2 0 = 1), in an individual Rr- 2 types (2 1 = 2), in an individual with the genotype ss- type 1 (2 0 = 1), in an individual with the genotype AaBb- 4 types of gametes (2 2 = 4):

a) one type of gametes

b) two types of gametes

c) one type of gametes

d) four types of gametes

Task 3. A male individual has a genotype Nn.

What types of sperm are produced in this individual?

What is the numerical ratio of spermatozoa different types, formed in an individual with the genotype Nn?

What biological process regulates this ratio?

Solution . Two types of sperm with genes N And n in a ratio of 1:1 (50% each). This relationship is based on an equally probable mechanism of chromosome and chromatid separation into anaphase of meiosis 1 and anaphase of meiosis 2.

Self-control tasks

Task 1. How many types of gametes form:

a) homozygous individual with one dominant trait;

b) heterozygous individual for one trait;

c) an individual with one recessive trait?

Problem 2. If female body with genotype mm gene M during meiosis it entered the egg, where the gene will go m?

Task 3. In humans, brown eye color is dominant over blue:

1. How many types of eggs, differing in a given pair of genes, are formed in a heterozygous brown-eyed woman?

2. How many types of sperm does a blue-eyed man produce?

Problem 4. How many types of gametes and which ones are formed by organisms that have genotypes: a) AA; b) AABB; V) aaBB; G) aaww?

Task 5. How many types of gametes and which ones are formed by the following organisms:

a) monohybrid by gene A;

b) dihybrid by genes A And IN;

c) trihybrid by genes A, B, WITH?

Task 6. How many types of gametes does an organism produce?

a) heterozygous for one pair of genes;

b) heterozygous for two pairs of genes;

c) heterozygous for four pairs of genes;

d) heterozygous for n pairs of genes?

Task 7. How many types of gametes and which ones exactly form organisms with genotypes:

A) MmNnSsRr; b) MMnnssRR; V) DdeeFfHH?

Task 8. In a person, brown eye color dominates over blue, and myopia dominates over normal vision. How many types of gametes and which ones exactly are produced by a diheterozygous brown-eyed myopic woman?

Chapter 2. MONOHYBRID CROSSING

Basic theoretical principles

Crossing in which organisms are analyzed according to one alternative (qualitative) trait is called monohybrid.

FirstthMendel's law -law of uniformity first generation hybrids. Statement of the law: When crossing homozygous individuals analyzed according to one alternative (qualitative) trait, uniformity of the first generation hybrids in phenotype and genotype is observed.

For this law there are no conditions limiting its action (always when homozygotes are crossed, the offspring are uniform).

Mendel's second law (law of splitting ) is formulated as follows: when crossing heterozygous organisms analyzed according to one alternative (qualitative) trait, in the first generation a splitting ratio of 3:1 by phenotype and 1:2:1 by genotype is observed.

This law has conditions limiting its operation:

all types of intra-allelic interaction of genes, except for complete dominance;

lethal and semi-lethal genes;

unequal probability of formation of gametes and zygotes of different types;

gene penetrance is less than 100%;

pleiotropic action of genes.

To determine the genotype of an individual with a dominant trait (with complete dominance of the homozygote AA and heterozygote Ahh phenotypically indistinguishable) are used test cross , in which an organism with a dominant trait is crossed with an organism that has a recessive trait.

There are two possible crossbreeding results.

If, as a result of crossing, uniformity of first-generation hybrids is obtained, then the analyzed organism is homozygous, and if a 1:1 split occurs in F 1, then the individual is heterozygous.

(sex cells) that come together during sexual reproduction to form a new cell called a zygote. Male gametes are sperm, and female gametes are eggs. In seed plants, pollen is the male sperm that produces the gametophyte. Female gametes (eggs) are contained within the ovary of the plant. In animals, gametes are produced in male and female. Spermatozoa are motile and have a long tail-like outgrowth. However, the eggs are not motile and are relatively large compared to the male gamete.

Gamete formation

Gametes are formed through cell division called. This two-step division process produces four, which are haploid. contain only one set. When haploid male and female gametes combine in a process called fertilization, they form a zygote. The zygote contains two sets of chromosomes.

Types of gametes

Some male and female gametes are the same size and shape, while others differ in size and shape. In some species of algae, both male and female algae are almost identical, and are usually equally mobile. The combination of these gamete types is known as . In some organisms, gametes have different sizes and shapes, and their fusion is called heterogamy. Higher plants, animals, as well as some species of algae and fungi, exhibit a special type of anisogamy called. In oogamy, the female gamete is not mobile and is much larger than the male gamete.

Gametes and fertilization

Occurs when male and female gametes fuse. In animal organisms, the union of sperm and egg occurs in the fallopian tubes of the female reproductive tract. Millions of sperm are released during sexual intercourse and travel from the vagina into the fallopian tubes.

Sperm is specially adapted to fertilize an egg. The head region has a cap-like covering called the acrosome, which contains enzymes that help the sperm cell penetrate the gonad (the outer covering of the egg cell membrane). Upon reaching the egg, the sperm head fuses with the egg. Penetration through the zona pellucida (the membrane around the egg membrane) causes the release of substances that alter the zona pellucida and prevents other sperm from fertilizing the egg. This process is critical because fertilization by multiple sperm cells, or polyspermy, produces a zygote with extra chromosomes. This phenomenon is fatal to the zygote.

After fertilization, two haploid gametes become one diploid cell or zygote. In humans, this means that the zygote will have 23 pairs per total 46 chromosomes. The zygote will continue to divide through and eventually mature into a fully functioning organism. inheritance of sex chromosomes. Sperm cells can have one of two types of sex chromosomes - X or Y. An egg has only one type of sex chromosome - X. If a sperm cell with a Y chromosome fertilizes an egg, the resulting individual will be male (XY). If a sperm cell with an X chromosome fertilizes an egg, the resulting individual will be female (XX).

23. How many types of gametes and which ones are formed by the following organisms:

a) an organism with genotype AA?

b) an organism with the AABB genotype?

c) an organism with the aaBB genotype?

d) is the organism recessive for genes a and b?

24. How many types of gametes and which ones are formed by the following organisms:

a) monohybrid Aa?

b) dihybrid AaBb?

c) trihybrid AaBbCc?

25. How many types of gametes do organisms form:

a) heterozygous for one pair of genes?

b) heterozygous for two pairs of genes?

c) heterozygous for four pairs of genes?

d) heterozygous for n pairs of genes?

26. How many types of gametes and which ones are formed by the following organisms:

a) an organism with the MmNnRrSS genotype?

b) an organism with the MMnnRRss genotype?

c) an organism with the genotype DdeeFfНН?

27. In peas, the yellow color of the seeds dominates over the green, and the smooth surface of the seed dominates over the wrinkled one.

a) How many and what types of gametes does a homozygous yellow smooth pea produce?

b) How many and what types of gametes does a heterozygous yellow smooth pea produce?

c) How many and what types of gametes does a heterozygous yellow wrinkled pea produce?

d) How many and what types of gametes are produced by green peas that are heterozygous for a smooth surface?

28. In Drosophila grey colour body (V) dominates yellow (v), red eye color (S) dominates sepia color (s), and normal wings (B) dominate curved wings (b).

a) How many and what types of gametes does a fly with a yellow body, sepia-colored eyes and curved wings produce?

b) How many and what types of gametes does a dihybrid form, which has a gray body, red eyes and curved wings?

c) A fly with a yellow body is heterozygous for eye color and wing shape. What types of gametes does it form?

29. In humans Blue eyes(b) are recessive to brown (B), and myopia (M) dominates normal vision (m).

a) What types of eggs are produced by a blue-eyed woman with normal vision?

b) What types of sperm are produced by a brown-eyed, myopic man who is heterozygous for both genes?

30. In peas, the yellow color of the seeds (A) dominates over the green (a), the smooth surface of the seeds (B) dominates over the wrinkled surface (b).

a) Homozygous yellow smooth peas are crossed with green wrinkled peas. Determine the genotype and phenotype of the offspring in the first and second generations.

b) Diheterozygous yellow smooth peas are crossed with green wrinkled ones. What cleavage by genotype and phenotype is expected in the first generation?

d) Heterozygous yellow wrinkled peas are crossed with green heterozygous for smooth seed shape. What cleavage by genotype and phenotype is expected in the first generation?

31. In the Drosophila fly, the absence of eyes (gene - “e” - еуеless) is inherited as a recessive trait, and the normal structure of the wings (V) dominates the rudimentary wings (gene “v” - vetstigial).

a) An eyeless fly with normal wings, heterozygous for the vestigial allele, is crossed with a fly with normal eyes, heterozygous for the eyeless gene and with rudimentary wings. Determine the genotype and phenotype of their offspring.

b) Flies that are heterozygous for both genes are crossed. Determine segregation based on the phenotype of their offspring.

c) When crossing a fly with normal eyes and wings with an eyeless fly with normal wings, the following offspring were obtained: 3/8 with normal eyes and wings, 3/8 eyeless with normal wings, 1/8 with normal eyes and rudimentary wings and 1/ 8 eyeless with rudimentary wings. Determine the genotype of the parents.

32. In humans, myopia (M) dominates normal vision, and Brown eyes(B) – above the blue ones.

a) The only child of myopic, brown-eyed parents has blue eyes and normal vision. Determine the genotypes of all three members of this family.

b) A blue-eyed myopic woman from a marriage with a brown-eyed man with normal vision gave birth to a brown-eyed myopic child. Is it possible to determine the genotype of the parents?

c) A blue-eyed, myopic man, whose mother had normal vision, married a brown-eyed woman with normal vision. The first child from this marriage is brown-eyed and myopic. The second one is blue-eyed and myopic. Determine the genotypes of parents and children.

33. In humans, the presence of the “Rh factor” antigen in erythrocytes - the Rh+ phenotype, is caused by the dominant gene - D. Its allele-d determines the absence of this antigen (Rh- phenotype). The gene for the first (0) blood group (I0) is recessive to the gene for group II (IA) and group three (IB). The last two alleles are codominant, their combination (IAIB) determines blood group IV.

a) The genotype of the husband is ddIAI0, the wife is DdIBIB. What is the probability of having a Rh-positive child of group IV?

b) A Rh-positive woman of group II, whose father had Rh-negative blood of group I, married a Rh-negative man of group I. What is the probability that the child will inherit both characteristics of the father?

c) A man with Rh-negative blood of group IV married a woman with Rh-positive blood of group III. The wife's father had Rh-negative blood of group I. Two children were born into the family. The first has Rh-negative blood of group III, the second has Rh-positive blood of group I. A forensic examination determined that one of these children was illegitimate. Which of the two pairs of alleles excludes paternity?

34. In humans, antigens of the ABO system are determined by multiple allelomorphs I 0, I A and I B; Rh antigen of erythrocytes (Rh+ and Rh- - alleles D and d, respectively); MN blood group system – codominant alleles LM and LN.

a) How many different phenotypes according to the three blood group systems exist in people, if we take into account all possible combinations of ABO, Rh and MN antigens?

b) The genotype of the mother is I A I 0 DdLMLM, the genotype of the father is I A I B ddLMLM. How many and what combinations of antigens are possible in their children?

c) The mother’s genotype is I 0 I 0 DdLNLN, and the father’s is I A I B ddLMLM. How many different phenotypes and what phenotypes are possible in their children?

d) A woman with the ARh-MN phenotype, whose father had blood group I, married a man whose blood contains ABRh+N antigens. The man's mother was Rh negative. Establish the probability that the child will have the same combination of antigens as the father.

e) The phenotype of the mother is ABMRh-, the father is OMRh+. One of my father's parents was Rh negative. How many and what combinations of blood antigens are possible in their children? How many combinations from the total number of possible combinations for the three blood group systems (ABO, MN, Rh+, Rh-) are excluded?

f) The forensic medical expert is tasked with finding out whether the boy in the family of the spouses R is a relative or adopted son these spouses.

A blood test of all three family members gave the following results. The woman has Rh-positive blood of group IV with the M antigen. Her husband has Rh-negative blood of group I with the N antigen. The child has Rh-positive blood of group I with the M antigen. What conclusion should the expert give and how will it be justified?