(sex cells) that unite 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. The 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 immobile and relatively large compared to the male gamete.

gamete formation

Gametes are formed through cell division called. This two-step fission process produces four that 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 are almost identical, and are usually equally mobile. The union of these types of gametes is known as . In some organisms, gametes have different sizes and shapes, and their fusion is called or heterogamy. Higher plants, animals, as well as some types of algae and fungi exhibit a special type of anisogamy called. In oogamy, the female gamete is immobile and 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 intercourse, which travel from the vagina to the fallopian tubes.

Sperm is specifically designed to fertilize an egg. The head region has a cap-like covering called the acros, which contains enzymes that help the sperm cell to penetrate the gonad (outer membrane covering of the egg cells). Upon reaching the egg, the sperm head fuses with the egg. Penetration through the zona pellucida (sheath around the membrane of the egg) causes the release of substances that change the zona pellucida and prevents other sperm from fertilizing the egg. This process is critical since 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 for a total of 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 cell 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 form the following organisms:

a) an organism with the AA genotype?

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 form the following organisms:

a) monohybrid Aa?

b) AaBb dihybrid?

c) AaBbCs trihybrid?

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 DdeeFfHH?

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 form?

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

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

d) How many and what types of gametes does green pea form, heterozygous for a smooth surface?

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

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

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 in relation 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 spermatozoa does a brown-eyed myopic man heterozygous for both genes produce?

30. In peas, the yellow color of the seeds (A) dominates over the green (a), the smooth surface of the seeds (B) - over the wrinkled (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 pea crossed with green wrinkled. What splitting by genotype and phenotype is expected in the first generation?

d) A heterozygous yellow wrinkled pea is crossed with a green heterozygous for the smooth seed shape. What splitting by genotype and phenotype is expected in the first generation?

31. In Drosophila flies, the absence of eyes (gene - "e" - eyeless) is inherited as a recessive trait, and the normal structure of wings (V) dominates over 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) Crossed flies heterozygous for both genes. Determine the splitting by the phenotype of their offspring.

c) When a fly with normal eyes and wings was crossed with an eyeless fly with normal wings, 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 8 eyeless with rudimentary wings. Determine the genotype of the parents.

32. In humans, myopia (M) dominates over normal vision, and brown eyes (B) dominate over 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 had a brown-eyed myopic child. Is it possible to determine the genotype of the parents?

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

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

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

b) 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 traits from 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 group I. Two children were born in the family. The first has Rh-negative blood of group III, the second - Rh-positive blood of group I. A forensic medical examination determined that one of these children was illegitimate. Which of the two pairs of alleles rules out paternity?

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

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

b) Mother's genotype - I A I 0 DdLMLM, father's - 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 genotype 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 the I blood group, married a man whose blood contains the 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 out of the total number possible according to the three systems of blood groups (ABO, MN, Rh+, Rh-) are excluded?

f) The forensic expert was tasked to find out whether the boy in the family of the spouses P is the natural or adopted son of these spouses.

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

Genotype- it is a set of genes received by an organism from its parents.

Phenotype - it is a combination of all the properties and characteristics of an organism that develop on the basis of the genotype in certain environmental conditions.

A single feature is called hair dryer(eye color, nose shape, stomach volume, red blood cell count, etc.).

The main patterns of inheritance were studied by G. Mendel. They are present 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 a pair of allelic genes enters the gamete.

Chapter 1

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

When writing out gametes, you need to know that:

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

if the organism is homozygous (for example, AA), then all gametes, no matter how many are formed, will contain only one gene ( BUT), 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 Ah), then in the process of meiosis one chromosome with a gene BUT will fall into one gamete, and the second homologous chromosome with the gene a gets into another gamete, therefore, a heterozygous organism for one pair of genes will form two types of gametes;

formula for writing out gametes N = 2 n , where N is the number of gamete types, and n is the number of traits for which the organism heterozygous.

Solution of typical tasks

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

Solution . From each homologous pair of chromosomes, one gets into the gamete. Choosing 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 it doubles, etc. In total, we have 222......... 2 = 2 23 = 8  10 6 gamete variants.

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 determine the number of types of gametes 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- 1 type (2 0 = 1), in an individual with the genotype AaBb- 4 types of gametes (2 2 = 4):

a) one type of gamete

b) two types of gametes

c) one type of gametes

d) four types of gametes

Task 3. The male has a genotype Nn.

What types of spermatozoa are produced in this individual?

What is the numerical ratio of spermatozoa of 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 ratio is based on the equiprobable mechanism of chromosome and chromatid segregation into meiotic anaphase 1 and meiotic anaphase 2.

Tasks for self-control

Task 1. How many types of gametes form:

a) a homozygous individual with one dominant trait;

b) a heterozygous individual for one trait;

c) an individual with one recessive trait?

Task 2. If a female body with the genotype mm gene M during meiosis, got into the egg, where the gene will go m?

Task 3. In humans, brown eyes dominate over blue:

1. How many types of eggs that differ in this pair of genes are formed in a heterozygous brown-eyed woman?

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

Task 4. How many types of gametes and which ones form organisms that have genotypes: a) AA; b) AABB; in) aaBB; G) aavv?

Task 5. How many types of gametes and which ones form the following organisms:

a) monohybrid by gene BUT;

b) gene dihybrid BUT and AT;

c) trihybrid by genes A, B FROM?

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

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

a) MmNnSsRr; b) MMnnssRR; in) 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 does a diheterozygous brown-eyed myopic woman form?

Chapter 2. MONOHYBRID CROSSING

Basic theoretical provisions

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

firstthMendel's law -law of uniformity first generation hybrids. The wording of the law: when crossing homozygous individuals analyzed for one alternative (qualitative) trait, uniformity of hybrids of the first generation in terms of phenotype and genotype is observed.

F 1 .	Aa - 100%

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

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

F 1 .	AA; Ah; Ah; aa.

There are conditions for this law that limit its operation:

all varieties 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 less than 100%;

pleiotropic action of genes.

To determine the genotype of an individual with a dominant trait (with complete dominance of the homozygous AA and heterozygous Ah phenotypically indistinguishable) are used analyzing cross in which an organism with a dominant trait is crossed with an organism that has a recessive trait.

There are two options for crossover results.

F 1 .					F 1 .	Ah; aa

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