Most animals are dioecious organisms. Sex can be considered as a set of characteristics and structures that provide a method of reproduction of offspring and transmission hereditary information. Sex is most often determined at the time of fertilization, that is, the karyotype of the zygote plays a major role in determining sex. The karyotype of each organism contains chromosomes that are the same in both sexes - autosomes, and chromosomes on which the female and male sexes differ from each other - sex chromosomes. In humans, the “female” sex chromosomes are two X chromosomes. When gametes are formed, each egg receives one of the X chromosomes. A sex that produces gametes of the same type, carrying the X chromosome, is called homogametic. In humans, the female sex is homogametic. The “male” sex chromosomes in humans are the X chromosome and the Y chromosome. When gametes are formed, half of the sperm receives an X chromosome, the other half receives a Y chromosome. Sex that produces gametes different types, is called heterogametic. In humans, the male sex is heterogametic. If a zygote is formed that carries two X chromosomes, then a female organism will be formed from it, if an X chromosome and a Y chromosome will form a male organism.
In animals the following can be distinguished: four types of chromosomal sex determination.
Inheritance of sex-linked traits
It has been established that sex chromosomes contain genes responsible not only for the development of sexual characteristics, but also for the formation of non-sexual characteristics (blood clotting, color of tooth enamel, sensitivity to red and green colors, etc.). The inheritance of non-sexual characteristics, the genes of which are localized on the X or Y chromosomes, is called sex-linked inheritance.
T. Morgan studied the inheritance of genes localized on sex chromosomes.
In Drosophila, red eye color is dominant over white. Reciprocal crossing- two crossings, which are characterized by a mutually opposite combination of the analyzed trait and sex in the forms taking part in this crossing. For example, if in the first crossing the female had a dominant trait and the male had a recessive trait, then in the second crossing the female should have a recessive trait and the male should have a dominant one. Carrying out reciprocal crossing, T. Morgan obtained the following results. When red-eyed females were crossed with white-eyed males in the first generation, all offspring turned out to be red-eyed. If you cross F1 hybrids with each other, then in the second generation all the females turn out to be red-eyed, and among the males, half are white-eyed and half are red-eyed. If you cross white-eyed females and red-eyed males, then in the first generation all the females turn out to be red-eyed, and the males are white-eyed. In F 2, half of the females and males are red-eyed, half are white-eyed.
T. Morgan was able to explain the results of the observed splitting in eye color only by assuming that the gene responsible for eye color is localized on the X chromosome (X A - red eye color, X a - White color eyes), and the Y chromosome does not contain such genes.
| R | ♀X A X A red-eyed |
× | ♂X a Y white-eyed |
| Types of gametes | X A | X a Y | |
| F 1 | X A X a ♀ red-eyed 50% |
X A Y ♂ red-eyed 50% |
| R | ♀X A X a red-eyed |
× | ♂X A Y red-eyed |
|
| Types of gametes | X A X a | X A Y | ||
| F 2 | X A X A X A X a ♀ red-eyed 50% |
X A Y ♂ red-eyed 25% |
X a Y ♂ white-eyed 25% |
|
| R | ♀X a X a white-eyed |
× | ♂X A Y red-eyed |
| Types of gametes | Xa | X A Y | |
| F 1 | X A X a ♀ red-eyed 50% |
X a Y ♂ white-eyed 50% |
| R | ♀X A X a red-eyed |
× | ♂X a Y white-eyed |
||
| Types of gametes | X A X a | X a Y | |||
| F 2 | X A X A ♀ red-eyed 25% |
X a X a ♀ white-eyed 25% |
X A Y ♂ red-eyed 25% |
X a Y ♂ white-eyed 25% |
|
Diagram of human sex chromosomes and genes linked to them:
1 - X chromosome; 2 - Y chromosome.
In humans, a man receives an X chromosome from his mother and a Y chromosome from his father. A woman receives one X chromosome from her mother and another X chromosome from her father. X chromosome is medium submetacentric, Y chromosome is small acrocentric; The X chromosome and Y chromosome have not only different sizes, structure, but also for the most part carry different sets of genes. Depending on the gene composition in human sex chromosomes, the following regions can be distinguished: 1) non-homologous region of the X chromosome (with genes found only on the X chromosome); 2) a homologous region of the X chromosome and the Y chromosome (with genes present on both the X chromosome and the Y chromosome); 3) a non-homologous section of the Y chromosome (with genes found only on the Y chromosome). Depending on the location of the gene, they are in turn distinguished following types inheritance.
| Inheritance type | Gene localization | Examples |
|---|---|---|
| X-linked recessive | Hemophilia, different shapes color blindness (protanopia, deuteronopia), absence of sweat glands, some forms of muscular dystrophy, etc. | |
| X-linked dominant | Non-homologous region of the X chromosome | Brown tooth enamel, vitamin D resistant rickets, etc. |
| X-Y - linked (partially linked to the floor) | Homologous region of the X and Y chromosomes | Alport syndrome, general color blindness |
| Y-linked | Non-homologous region of the Y chromosome | Webbed toes, hypertrichosis of the auricular margin |
Most of the genes linked to the X chromosome are absent from the Y chromosome, so these genes (even recessive ones) will manifest themselves phenotypically, since they are represented in the genotype in singular. Such genes are called hemizygous. The human X chromosome contains a number of genes, the recessive alleles of which determine the development of severe anomalies (hemophilia, color blindness, etc.). These anomalies are more common in men (since they are hemizygous), although the carrier of the genes causing these anomalies is more often a woman. For example, if X A is normal blood clotting, X a is hemophilia, and if a woman is a carrier of the hemophilia gene, then phenotypically healthy parents a hemophilic son may be born.
Genetics of sex. Sex-linked inheritance.
Target: to form in students an idea of the genetics of sex, the inheritance of sex-linked traits.
Tasks:
1. Educational: form the concepts: autosomes, heterochromosomes, homogametic, heterogametic sex, form an idea of the determination of sex development, sex-linked traits, traits inherited through the Y chromosome and X chromosome; To introduce students to the peculiarities of inheritance of sex chromosomes, some pathological human conditions that are inherited in a sex-linked manner.
2. Developmental: continue the formation of skills in solving genetic problems for linked inheritance of genes, for inheritance linked to sex, develop mental operations.
3. Educational: to form conscious attitude to your health and the health of your descendants.
Equipment: computer, multimedia projector, screen ( interactive board), Power Point presentation.
Lesson type: lesson on learning a new topic.
Genetics of sex
Genetics has explained the essence of an amazing and important problem: equal distribution of female and male individuals in generations of animals and people
· Which method of reproduction is characterized by the formation of gametes? Sexual
· What set of chromosomes do they have? n
· What is the name of a fertilized egg, and what set of chromosomes does it have? Zygote, 2n
First, let's remember what the chromosome set of human cells is.
How many chromosomes does a human karyotype have? of 46 chromosomes
44 are the same in all individuals, regardless of gender (these chromosomes are called autosomes), and women differ from men in one pair of chromosomes, called sex chromosomes. This is a general biological pattern for all living organisms that reproduce sexually.
Autosomes- paired chromosomes, the same for both male and female organisms.
Sex chromosomes– chromosomes, the set of which distinguishes male and female individuals in animals and plants with chromosomal sex determination.
Diploid cell of the human body: 46 chromosomes = 23 pairs of homologous chromosomes, of which 22 pairs are autosomes + 1 pair of sex chromosomes:
· How are sex chromosomes designated? for a man - XY; for a woman - XX.
Sex can be considered as one of the characteristics of an organism, usually determined by genes. The mechanism for determining sex has a different character - chromosomal.
Chromosomal sex determination mechanism
The sex of the future offspring is determined by the combination of sex chromosomes. A sex that has the same sex chromosomes is called homogametic , since it gives one type of gametes, and those with different ones - heterogametic, since it produces two types of gametes. In humans, mammals, and Drosophila flies, the homogametic sex is female, and the heterogametic sex is male. Heterogametic female in birds, reptiles
· In the male sex, during the process of gametogenesis, 2 types of gametes are formed in equal proportions, since the male sex is heterogametic: X-sperm and Y-sperm.
· Since the female sex has the same sex chromosomes, since the female sex is homogametic, each egg carries an X chromosome.
Theoretically, the sex ratio should be 1:1. This is a statistical pattern ensured by the condition of equally probable meeting of gametes. Statistically, this is what happens.
· Do you think homogametic or heterogametic sex will determine gender?
The sex of the future organism always determines heterogametic sex(i.e. male), precisely because gametes with the X- and Y-chromosomes are formed in the male sex in equal quantities.
The X and Y chromosomes differ in structure: the Y chromosome consists of two sections - one homologous to the X chromosome, and the other non-homologous. And also by the set of genes that are found in them.
Chromosomal sex determination. Since ancient times, humanity has been interested in the question: why do the same parents have offspring of different sexes and why do most dioecious organisms have approximately the same ratio of male and female individuals? Hundreds of hypotheses were put forward, but only the development of genetics and cytology made it possible to reveal the mechanism of inheritance and sex determination.
Floor is a set of morphological, physiological, biochemical and other characteristics of an organism that ensure the reproduction of its own kind. Let us remember that sexual characteristics are usually divided into primary (the presence of gonads of a certain type and other reproductive organs) and secondary (phenotypic differences between male and female individuals that are not directly involved in the reproductive process). Since traits are determined by genes, it has been assumed that the sex of an organism is determined genetically.
When studying the karyotypes of many species of animals and humans, it was found that male and female individuals have differences in one pair of chromosomes. Further research showed that these chromosomes determine the sex of the organism, and therefore they received the name sex chromosomes. All other pairs of chromosomes (the same in males and females) were named autosomes.
In somatic cells person contains 23 pairs of chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes. In the cells of the male body, sex chromosomes differ sharply in size and structure. One of them is large, unequal-armed, contains a large number of genes are X chromosome(x) (Fig. 100). The other chromosome is small, resembles the letter Y and contains relatively few genes. She is named Y chromosome(Greek). IN In the cells of the female body, the sex chromosomes are the same - two X chromosomes.
Labeling autosomes with a letter A, you can write the chromosome set of a woman as 44 A+XX, men - 44 A+XY. When gametes are formed, each of them contains half of the autosomes and one of the sex chromosomes. This means that one type of egg is formed in the female body: they all have a set of chromosomes 22A+X. In the male body, two types of sperm are formed: equal ratio: 22A+X and 22L + U.
If an egg is fertilized by a sperm containing an X chromosome, the zygote develops into a female body. If a sperm with chromosome 7 is involved in fertilization, a male child develops from the zygote. Therefore, in a person, the sex of the child depends on the type of sperm of the father. Since both types of male gametes are produced with equal probability, the offspring exhibits gender split 1:1.
Same as person, sex determination occurs in most others mammals, row insects(for example, at fruit flies), many dioecious plants. For example, in somatic cells fruit flies there are 4 pairs of chromosomes: 3 pairs of autosomes and 1 pair of sex chromosomes (Fig. 101).
Chromosome set of females fruit flies 6A+XX, males - 6 A + XY.
A sex that has identical sex chromosomes and produces the same type of gametes is usually called homogametic.
A sex that produces two types of gametes is called heterogametic. With the XY type of sex determination, the female sex is homogametic, and the male sex is heterogametic (Fig. 102).
In nature, the opposite type of sex determination is also found, in which males are homogametic and females are heterogametic. This is typical, for example, for birds(see Fig. 102), many reptiles, some fish, amphibians, butterflies (silkworm), plants (strawberries). In this case, sex chromosomes are designated by the letters Z and W, to highlight this type gender determination. In males, sex chromosomes are written as ZZ, and in females — ZW.
U In some species of living organisms, the heterogametic sex has only one unpaired sex chromosome, while the homogametic sex has two identical ones. For example, at grasshopper females have a chromosome set of 16A + XX, and males - 16A + AT) (zero indicates the absence of a chromosome). Females are homogametic, their eggs contain nine chromosomes: 8A +X. Males produce two types of sperm: some also contain nine chromosomes: 8A+X, in others there are only eight: 8A + 0. Therefore, grasshopper The male sex is heterogametic. X0 type of sex determination is also found in other species Orthoptera, as well as beetles, spiders, some bedbugs, roundworms. In cases where the heterogametic sex is female, the sex chromosomes of females are written as Z0, and of males - ZZ.
In bees, wasps, ants and some others Hymenoptera's no sex chromosomes. Females are diploid organisms that develop from fertilized eggs, and haploid males develop from unfertilized ones (see Fig. 102).
Peculiarities of inheritance of sex-linked traits. Sex chromosomes contain not only genes that determine the sex of an organism, but also others that are not related to sex. For example, the human X chromosome contains genes that control blood clotting, color perception (the ability to distinguish primary colors), the development of the optic nerve, etc. The 7th chromosome does not contain these genes.
The human F chromosome has small sizes and accordingly contains fewer genes than X- chromosome. However, in addition to the genes that determine the development of male sexual characteristics, it also contains others. Exactly at Y- chromosome contains genes that determine the presence of coarse hair on ears, large teeth and some other signs. There are no such genes on the A^ chromosome, so these signs can only appear in men.
Traits that are determined by genes located on the sex chromosomes are called gender-linked characteristics. The inheritance of these characteristics has its own characteristics. Let's consider them using the example of a hereditary human disease - hemophilia.
People with hemophilia have impaired blood clotting, so life-threatening bleeding may occur as a result of injury or surgery. In addition, hemophiliacs often experience spontaneous hemorrhages in the joints and internal organs.
This disease is caused by a recessive gene /r, linked to the X chromosome. Dominant gene N determines normal blood clotting in a person. Women have two X chromosomes, therefore, based on blood clotting, as well as other characteristics linked to the X chromosome, three genotype options are possible:
Girls with hemophilia are extremely rare: one per 100 million newborns (among boys this figure is much higher, on average 1: 10,000). Previously, many hemophiliac girls died in adolescence in connection with the onset of menstruation. Although hemophilia is still considered incurable disease, its course is controlled by injections of the missing clotting factor. Thus, modern medicine significantly extends the life expectancy of patients with hemophilia.
When recording crosses, chromosome 7 is designated by a line with a hook:
Regarding genes N or h it is "empty". Therefore, a man has only one gene that determines blood clotting. This gene is located on the X chromosome and is always expressed in the phenotype, regardless of whether it is dominant or recessive. Thus, men may have the following genotypes:
As can be seen from the genotype records, men cannot be carriers of the gene for hemophilia and other hereditary diseases linked to the X chromosome.
Let's consider what kind of offspring can appear in a woman who is a carrier of the hemophilia gene and a man with normal blood clotting:
So, among the sons there is a split according to genotype and phenotype: half are healthy, half are hemophiliacs. Among the daughters, there is a split according to genotype: all of them are healthy, but half are carriers of the hemophilia gene. A similar pattern is characteristic of other sex-linked recessive traits. These include, for example, hereditary diseases such as low blood pressure, optic nerve atrophy, and absence of sweat glands.
In order for a girl to be born with a recessive trait linked to the X chromosome, it is necessary to combine two recessive genes in the zygote - from the mother and from the father. To manifest the same trait in a boy, one recessive gene received from the mother is enough (since the father passes only the 7th chromosome to his son). Therefore, X-linked recessive traits are more common among men. For example, in Europe more than 6% suffer from color blindness male population, while among women this disease occurs with a frequency of approximately 0.5%.
Genotype as complete system. By studying the patterns of inheritance of traits in organisms, you became familiar with different types of interaction allelic genes. In some cases, the result of such interaction may be the appearance of a qualitatively new trait that was not determined by any of the genes separately (remember, for example, what determines blood group IV in humans).
However, in living organisms a huge number of traits are known that are controlled not by one, but by two or more pairs of genes. The interaction of non-allelic genes determines, for example, height, body type and skin color in humans, the color of fur and plumage in many mammals and birds, the shape, size, color of fruits and seeds of plants, etc. The opposite phenomenon is often observed, when one pair of allelic genes affects several signs of the body at once. In addition, the action of some genes can be changed by the proximity of other genes or conditions environment.
Thus, the genes are closely related and interact with each other. Therefore, the genotype of any organism cannot be considered as simple sum individual genes. A genotype is a complex integral system of interacting genes.
1. What set of sex chromosomes is characteristic of male somatic cells? Women? Rooster? Chicken?
ZZ, ZW, WW, XX, XY, YY.
2. Why do most dioecious animals have approximately the same number of male and female offspring?
3. The chimpanzee egg contains 23 autosomes. How many chromosomes does the chimpanzee karyotype have?
4. What signs are called sex-linked? What are the features of inheritance of these traits?
5. Prove that the genotype of a living organism is an integral system.
6. Color blindness is a recessive trait linked to the X chromosome. In a family where the mother has normal color perception, a color-blind daughter was born. Determine the genotypes of the parents. What is the likelihood of them having a healthy son?
7. In the polar owl, feathered legs dominate over bare legs. This trait is controlled by autosomal genes. Long claws are a dominant trait that is determined by a gene localized on the Z chromosome. A female with feathered legs was crossed with a male with long claws and feathered legs. As a result, we obtained offspring with various combinations all phenotypic traits. What is the probability (%) of a male with bare legs and short claws appearing among the offspring?
8. In one of the butterfly species, the heterogametic sex is female. A red male with club-shaped antennae was crossed with a yellow female with thread-like antennae. Half of the offspring were yellow males with threadlike antennae, the other half were red females with threadlike antennae. How are body color and antennae type inherited? What signs dominate? Establish the genotypes of the crossed forms and their offspring.
- § 1. Content of chemical elements in the body. Macro- and microelements
- § 2. Chemical compounds in living organisms. Inorganic substances
- § 10. History of the discovery of the cell. Creation of cell theory
- § 15. Endoplasmic reticulum. Golgi complex. Lysosomes
Chapter 1. Chemical components living organisms
Chapter 2. Cell - structural and functional unit living organisms
Chapter 3. Metabolism and energy conversion in the body
Genetic sex determination
1. Which chromosomes are called sex chromosomes?
2. What organisms are called hermaphrodites?
3. What diseases are called hereditary?
Theory of sex inheritance.
The vast majority of animal species are represented by individuals two genders- male and female. Segregation by gender occurs in a 1:1 ratio. In other words, in all species the number of males and females is approximately the same. Even G. Mendel drew attention to the fact that such splitting in the offspring according to any trait is observed in cases where one of the parent individuals was heterozygous (Aa) for this trait, and the second was a recessive homozygote (aa). It was assumed that one of the sexes (at that time it was unclear which one) was heterozygous, and the second was homozygous for the gene that determines the sex of the organism.
The modern theory of sex inheritance was developed by T. Morgan and his colleagues at the beginning of the 20th century. They were able to establish that males and females differ in their set.
In male and female organisms, all pairs of chromosomes, except one, are identical and are called autosomes, and one pair of chromosomes, called sex chromosomes, differs in males and females. For example, both male and female fruit flies have three pairs of autosomes in each cell, but the sex chromosomes differ: females have two X chromosomes, and males have X and Y (Fig. 62). The sex of the future individual is determined during fertilization. If the sperm contains an X chromosome, then a female (XX) will develop from the fertilized egg, and if the sperm contained a sex Y chromosome, then a male (XY).
Since female Drosophila produces only eggs containing sex X chromosomes, the female sex in Drosophila is called homogametic. In male Drosophila, spermatozoa with either X or Y sex chromosomes are formed in equal proportions. Therefore, the male sex in Drosophila is called heterogametic.
In many species of living beings, for example, crustaceans, amphibians, fish, and most mammals (including humans), the female sex is homogametic (XX), and the male is heterogametic (XY).
The inheritance of sex in humans can be represented in the form of a diagram (Fig. 63). Obviously, the sex ratio at this crossing theoretically it will always be 1:1.
In humans, the Y chromosome, which determines male sex, is passed from father to son at the time of fertilization. Thus, the sex of the baby depends only on which of the sex chromosomes got into the zygote from the father. The human Y chromosome contains genes for proteins necessary for normal development male gonads. These glands very quickly begin to secrete male sex hormones, which determine the formation of the entire male reproductive system. If a sperm with an X chromosome participated in fertilization, then the Y chromosome is absent in the cells of the developing embryo, which means there are no “male” proteins encoded by it. Therefore, in the embryo of a girl, the ovaries and female reproductive tract develop.
So, in Drosophila and humans, the female sex is homogametic, and general scheme The inheritance of sex is the same in these two species. In some species of living beings, chromosomal sex determination is completely different. For example, in birds and reptiles, males are homogametic (XX), and females are heterogametic (XY). In some insects, males have only one chromosome set sex chromosome(XO), and females are homogametic (XX).
Bees and ants do not have sex chromosomes, and females have a diploid set of chromosomes in their body cells, and males, which develop parthenogenetically (from unfertilized eggs), have a haploid set of chromosomes. Naturally, in this case, the development of sperm in males occurs without meiosis, since it is impossible to reduce the number of chromosomes of a less haploid set.
No sex chromosomes have been found in crocodiles. The sex of the embryo developing in the egg depends on the ambient temperature: at high temperatures More females develop, and if it is cool, more males.
Inheritance of sex-linked traits. The sex chromosomes contain a number of genes that are in no way related to sex-related traits. Traits whose genes are located on the sex chromosomes are called sex-linked. The nature of their inheritance depends on the principle genetic determination floor. As mentioned in the previous paragraph, in humans, the female sex is homogametic (XX), and the male sex is heterogametic (XY).
In humans, the Y chromosome is small, but in addition to the gene responsible for the development of male gonads, it contains a significant number of other genes, for example, a gene that determines the size of teeth.
But the X chromosome contains at least 200 genes. In the somatic cells of a woman there are two X chromosomes, so two genes are responsible for each trait, but in the cells of a man’s body there is only one X chromosome, and all one and a half hundred genes located in it - both dominant and recessive - are necessarily manifested in phenotype. Let’s assume that a “defective” X chromosome with some mutant gene that leads to the development of the disease entered the boy’s body from his mother. Since there is no second X chromosome in his cells (there is only a Y chromosome), the disease will definitely manifest itself. If such an X chromosome with a mutant gene gets into the egg from which a girl will develop, then she will not get sick, since she will receive from her father a normal X chromosome with a gene that will suppress the effect of the mutant one. According to the described scheme, a person inherits hemophilia - a disease in which the body lacks one of the substances necessary for blood clotting. With hemophilia, a person can bleed from even a minor cut or bruise.
This disease can be transmitted to a boy from healthy mother if she is a carrier of a pathological gene in one of the X chromosomes, and the paired allelic gene on the second X chromosome is normal (Fig. 64). In this case, the probability of giving birth to a sick boy is 50%. Girls suffer from hemophilia extremely rarely, since for this to happen, a healthy woman - a carrier of the hemophilia gene must give birth to a girl from a hemophilic man, and even in this case, the probability that the daughter will have hemophilia is 50%.
Just like hemophilia, color blindness is inherited - a congenital inability to distinguish between red and green colors, which, however, is not life-threatening.
Sex-linked traits. Autosomes. Sex chromosomes. Homogametic sex. Heterogametic sex.
1. What types of chromosomes do you know?
2. What is homogametic and heterogametic sex?
3. How is sex inherited in mammals?
4. What other options for chromosomal and non-chromosomal sex determination in living organisms do you know? Give specific examples
5. Is the male or female sex heterogametic in humans?
6. Are there differences in the number of chromosomes between the queen and worker honey bees?
The male gender is often called strong. However, from a genetic point of view this is not the case. The male body is less resistant to many adverse effects: infections, blood loss, stress, etc. In this regard, the gender ratio is 1; 1 in human populations is violated: for every 100 girls, 106 boys are born. The mechanism of this phenomenon is still unclear. By the age of 18, the ratio becomes normal - 1:1, by the age of 50, there are 85 men per 100 women, and by the age of 80 - only 50!
Kamensky A. A., Kriksunov E. V., Pasechnik V. V. Biology 10th grade
Submitted by readers from the website
Most animals are dioecious organisms. Sex can be considered as a set of characteristics and structures that provide a method of reproduction of offspring and the transmission of hereditary information. Sex is most often determined at the time of fertilization, that is, the karyotype of the zygote plays a major role in determining sex. The karyotype of each organism contains chromosomes that are the same in both sexes - autosomes, and chromosomes on which the female and male sexes differ from each other - sex chromosomes. In humans, there are two “female” sex chromosomes X-chromosomes. When gametes are formed, each egg receives one of X-chromosomes. A sex that produces gametes of the same type, bearing X-chromosome is called homogametic. In humans, the female sex is homogametic. "Male" sex chromosomes in humans - X-chromosome and Y-chromosome. When gametes are formed, half of the sperm receive X-chromosome, other half - Y-chromosome. A sex that produces different types of gametes is called heterogametic. In humans, the male sex is heterogametic. If a zygote is formed carrying two X-chromosome, then a female body will be formed from it if X-chromosome and Y- chromosome - male.
In animals the following can be distinguished: four types of chromosomal sex determination.
1. The female sex is homogametic ( XX), male - heterogametic ( XY) (mammals, in particular humans, Drosophila).
Genetic scheme chromosomal sex determination in humans:
2. The female sex is homogametic ( XX), male - heterogametic ( X0) (orthoptera).
Genetic scheme of chromosomal sex determination in the desert locust:
4. The female sex is heterogametic ( X0), male - homogametic ( XX) (some types of insects).
Genetic scheme of chromosomal sex determination in moths:
| R | ♀61, X0 | × | ♂62,XX |
| Types of gametes | 31, X 30, Y | 31, X | |
| F | 61, X0 females, 50% | 62, XX males, 50% |
End of work -
This topic belongs to the section:
Genetics
In all cases, analysis of the results showed that the ratio dominant traits to recessive in generation F was approximately... The above example is typical of all of Mendel's experiments in which... Based on these and similar results, Mendel drew the following conclusions...
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All topics in this section:
Reciprocal or analyzing crossing
An organism from the F1 generation, obtained from a cross between a homozygous dominant and a homozygous recessive individual, is heterozygous in its genotype, but has a dominant phenotype. For that
Dihybrid crossing and the law of independent distribution
Having established the ability to predict the results of crosses based on one pair of alternative traits, Mendel moved on to studying the inheritance of two pairs of such traits. Crosses between individuals
Brief summary of the essence of Mendel's hypotheses
· Every sign of a given organism controlled by a pair of alleles.
· If an organism contains two different alleles for a given trait, then one of them (dominant) can manifest itself completely
Chromosomal theory of heredity TO end of the 19th century
V. As a result of improving the optical qualities of microscopes and improving cytological methods, it became possible to observe the behavior of chromosomes in gametes and zygotes. Back in 1875 Gertvy
Clutch All situations and examples discussed so far have related to the inheritance of genes located on different chromosomes. As cytologists found out, a person has everything somatic cells
contain 46 chromosomes
Linkage groups and chromosomes, carried out at the beginning of our century, were mainly aimed at elucidating the role of genes in the transmission of traits. Morgan's work with the fruit fly Drosophila melanogaster so far
Giant chromosomes and genes
In 1913, Sturtevant began his work mapping the positions of genes on Drosophila chromosomes, 21 years before it became possible to link distinct chromosome structures to genes.
Determination of gender
Figure 1. Chromosome sets of male and female D. melanogaster. They consist of four pairs of chromosomes (pair I - sex
Incomplete dominance
There are cases where two or more alleles do not fully exhibit dominance or recessivity, so that in the heterozygous state, none of the alleles is dominant over the other. This is a phenomenon
Lethal genes
There are cases where one gene can influence several traits, including viability. In humans and other mammals, a certain recessive gene causes the formation
Epistasis
A gene is called epistatic (from the Greek epi - above) if its presence suppresses the effect of any gene located in another locus. Epistatic genes are sometimes called inhibitory genes, and
Variability
Variability is the totality of differences in one or another characteristic between organisms belonging to the same natural population or mind. Amazing morphological diversity
Discrete variability
Some traits in a population are represented by a limited number of variants. In these cases, the differences between individuals are clearly expressed, and there are no intermediate forms; such signs include, for example
Continuous variability
According to many characteristics in the population there is full row transitions from one extreme to another without any breaks. The most striking signs of frozen are such characteristics as mass (weight), linear dimensions
Environmental influence
Main factor, which determines any phenotypic trait, is the genotype. The genotype of an organism is determined at the moment of fertilization, but the degree of subsequent expression of this genetic potential
It must be clearly understood that the interaction between discrete and continuous variability and the environment makes it possible for two organisms with an identical phenotype to exist. Replication mechanism
Mutations
A mutation is a change in the amount or structure of DNA in a given organism. The mutation leads to a change in the genotype, which can be inherited by cells descending from the mutant cell in the re
Gene mutations
Sudden spontaneous changes in phenotype that cannot be associated with normal ones genetic phenomena or microscopic evidence of the presence of chromosomal aberrations, can only be explained by changes
The meaning of mutations
Chromosomal and gene mutations have a variety of effects on the body. In many cases, these mutations are lethal because they impair development; in humans, for example, about 20% of pregnancies end
Hereditary variability
Combinative variability. Hereditary, or genotypic, variability is divided into combinative and mutational.
Combinative is called variability, which is based on
Dihybrid cross
The essence of dihybrid crossing. Organisms differ in many genes and, as a result, in many traits. To simultaneously analyze the inheritance of several traits, it is necessary to study
Genetics methods
The main one is the hybridological method - a system of crossings that allows one to trace the patterns of inheritance of traits in a series of generations. First developed and used by G.
Genetic symbolism
Proposed by G. Mendel, used to record the results of crossings: P - parents; F - offspring, the number below or immediately after the letter indicates the ordinal number
The law of uniformity of first generation hybrids, or Mendel's first law
The success of Mendel's work was facilitated by the successful choice of the object for crossing - different varieties of peas. Features of peas: 1) it is relatively easy to grow and has a short development period
Law of segregation, or Mendel's second law
G. Mendel gave the first generation hybrids the opportunity to self-pollinate. The second generation hybrids obtained in this way showed not only a dominant, but also a recessive trait. Experience results
Law of gamete purity
From 1854, for eight years, Mendel conducted experiments on crossing pea plants. He discovered that as a result of crossing different varieties of peas with each other, first generation hybrids
Cytological basis of Mendel's first and second laws
At the time of Mendel, the structure and development of germ cells had not been studied, so his hypothesis of the purity of gametes is an example of brilliant foresight, which later found scientific confirmation.
The law of independent combination (inheritance) of characteristics, or Mendel's third law
Cytological basis of Mendel's third law
Let A be the gene that determines the development of yellow color of seeds, a - green color, B - smooth shape of the seed, b - wrinkled. Skr
Lecture No. 18. Chained inheritance
In 1906, W. Batson and R. Punnett, crossing sweet pea plants and analyzing the inheritance of pollen shape and flower color, discovered that these characters do not give independent distribution
Inheritance of sex-linked traits
It has been established that the sex chromosomes contain genes responsible not only for the development of sexual characteristics, but also for the formation of non-sexual characteristics (blood clotting, tooth enamel color, sensitivity to
Lecture No. 20. Gene interaction
Numerous experiments have confirmed the correctness of the patterns established by Mendel. At the same time, facts have appeared showing that the results obtained by Mendel numerical ratios when splitting hybri
TYPES OF INTERACTION OF ALLELIC GENES
There are complete dominance, incomplete dominance, codominance, and allelic exclusion.
Allelic genes are genes located at identical loci homolo
Complete Domination Complete Domination
Incomplete dominance
- this is a type of interaction of allelic genes in which the phenotype of heterozygotes does not differ from the phenotype of homozygotes in terms of the dominant, that is, in the phenotype of heterozygotes with
This is the name of the type of interaction of allelic genes in which the phenotype of heterozygotes differs from the phenotype
Codominance
Codominance is a type of interaction of allelic genes in which the phenotype of heterozygotes differs from both the phenotype of homozygotes for a dominant and the phenotype of homozygotes for a recessive, and
Complementarity
Epistasis
Complementarity is a type of interaction of non-allelic genes in which a trait is formed as a result of the total combination of the products of their dominant alleles. Occurs when inherited
Epistasis is a type of interaction of non-allelic genes in which one pair of genes suppresses (prevents the manifestation of the phenotype) another pair of genes.
The suppressor gene is called ep
Polymerism
This is a type of interaction between two or more pairs of non-allelic genes, the dominant alleles of which clearly affect the development of the same trait. The polymeric action of genes can be cumulative
Mutations
Lecture No. 21. Variability Variability is the ability of living organisms to acquire new characteristics and properties. Thanks to variability, organisms can adapt to changing environmental conditions. its organization, leading to changes in certain characteristics of the body
Gene mutations
Gene mutations are changes in the structure of genes. Since a gene is a section of a DNA molecule, a gene mutation represents changes in the nucleotide composition of this section
Chromosomal mutations
These are changes in the structure of chromosomes. Rearrangements can be carried out both within one chromosome - intrachromosomal mutations (deletion, inversion, duplication, insertion), and between chromosomes - inter
Genomic mutations
A genomic mutation is a change in the number of chromosomes. Genomic mutations occur as a result of disruption of the normal course of mitosis or meiosis.
Haploidy - y
Nondisjunction of sex chromosomes during meiosis in the mother
Nondisjunction of sex chromosomes during meiosis in the father
P ♀46, XX × ♂46, XY Types of gametes
The law of homological series of hereditary variability N.I. Vavilova
“Species and genera that are genetically close are characterized by similar series of hereditary variability with such regularity that, knowing a number of forms within one species, one can predict the finding of parallel
Artificial mutations Spontaneous mutagenesis occurs constantly in nature, but spontaneous mutations
- a fairly rare phenomenon, for example, in Drosophila, the white eye mutation is formed with a frequency of 1:100,000 gametes.
Factors in Modification variability Modifying variability is changes in the characteristics of organisms that are not caused by changes in the genotype and arise under the influence of factors
external environment
. Habitat plays bo Variation curve Based