What are the sex chromosomes in a chicken? Are humans as close to chickens as they are to chimpanzees? The human Y chromosome is as different from the chimpanzee Y chromosome as it is from the chicken chromosome.
The section on sex determination in butterflies and birds should begin with a small digression. In fact, we have just elucidated the method of determining sex in Drosophila and in animals in general and have emphasized its captivating simplicity and widespread distribution in the animal kingdom.
And here we are again faced with another mystery of nature, with a new complication of the question that interests us. It turns out that everything said above about sex determination by the Drosophila type is correct, but with one exception: this type of sex determination is not the only one in nature, common to all organisms. Along with it, there is another method, or type, of sex determination, first discovered in butterflies, and then in birds, including domestic chicken. Based on the name of the insect on which this type of sex determination was discovered for the first time, it is called the type of butterfly. Let's consider its features and differences from the Drosophila type. Let's take chickens as an object to describe the process: the reader is undoubtedly more familiar with them than with butterflies; and in the future we will have to deal with them more than once.
So, what is the difference between the mechanism of sex determination in birds and in Drosophila?
In Drosophila, as in all animals, males produce two types of sperm - with the X or Y chromosome, and in this sense they play a decisive role in determining the sex of future embryos. Females produce one type of egg - with an X chromosome.
In butterflies and birds, these relationships are diametrically opposed: in them the privilege of producing two types of reproductive cells belongs to females, as a result of which half of the eggs they lay (on females) contain one sex chromosome, and half of the eggs (on males) contain another, dissimilar sex chromosome . Male butterflies and birds produce one type of sperm. Consequently, their female sex is heterogametic, and their male sex is homogametic.
As for the divisions in the maturation of eggs and sperm, here they proceed in the same way as was described above for Drosophila and humans: the first of them, or the reduction division itself, proceeds according to the type of meiosis, and the second, or equational division, according to the type of mitosis .
In order to emphasize the difference in the methods of sex determination in Drosophila and animals, on the one hand, and in butterflies and birds, on the other, the sex chromosomes of the latter are sometimes designated by other letters, namely Z and W. According to this system, the sex chromosomes of a male are designated by the letters ZZ, and the female sex chromosomes are designated by ZW. Accordingly, one type of sperm produced by a rooster is designated by the letter Z, and two types of eggs produced by a hen are designated by the letters Z (for males) and W (for females).
However, following the precedents available in the literature, we will deviate from this rule and in the future we will adhere to a unified system for designating sex chromosomes, regardless of whether we are talking about determining sex by the Drosophila type or by the type of butterflies and birds. The point is not what letters to designate the sex chromosomes of the two groups of organisms being compared; it is more important to remember that, unlike Drosophila, in which the male sex is heterogametic, the female sex is heterogametic in butterflies and birds and that in them the sex of the embryos is established during the maturation of the eggs, i.e. even before fertilization.
At the same time, a unified system of designating sex chromosomes for all representatives of the animal world, with the exception of the noted polarity of types of sex determination, undoubtedly contributes to a more holistic and clear understanding of them.
Therefore, in the future, we will denote eggs of butterflies and birds as males by the letter X, and eggs as females by the letter Y. As for spermatozoa, here they are of the same type; We will denote them with the letter X. The process of spermatogenesis and oogenesis in butterflies and birds proceeds in exactly the same way as in Drosophila (see Fig. 14).
Further details of the process of sex determination in butterflies and birds are as simple as in Drosophila, and boil down to the following. If a mature egg, for example, of a chicken, contains an X chromosome, then after fertilization with an X sperm, it will develop into a cockerel (XX). If the egg contains a Y chromosome, then after fertilization (by the same sperm - they are all the same in roosters) a hen (XY) will develop (Fig. 24).
In accordance with the polarity of the mechanisms of sex determination in Drosophila and birds, the results of fertilization are also presented differently. In fact, in Drosophila, as we have seen, the sex of the embryo is determined at the moment of fertilization and in each individual case depends on the combination of sex chromosomes in the fertilized egg. Unlike Drosophila, in butterflies and birds, fertilization of the egg, figuratively speaking, only gives impetus to the development of the embryo of the same sex that is already inherent in it during the maturation process. Thus, every chicken egg is literally “destined” to develop into a chicken of exactly the same sex, and not the opposite sex.
It is also necessary to keep in mind that the cells of birds and butterflies, like all organisms, contain sets of autosomes in addition to sex chromosomes. The diploid number of chromosomes in a chicken is 78. Accordingly, half of the chicken eggs contain an X chromosome and 38 autosomes (X + 38) and half of the eggs contain a Y chromosome and the same number of autosomes (Y + 38). Rooster sperm are all the same - they contain an X chromosome and 38 autosomes (X + 38).
To what has been said above about sex determination in chickens, the following caveat must be made. The fact is that due to the presence of a large number of very small chromosomes in a chicken and the difficulties of counting and identifying them, the question of whether it has a Y chromosome has not yet been finally resolved, and it is possible that it is not there at all.
If in the future this turns out to be true, then everything said above about sex determination in chickens will remain in force, with the exception that the composition of the sex chromosomes of a chicken will need to be designated as XO, and the two types of eggs it produces, respectively, as X + 38 and 0 + 38 Under this condition, the total number of chromosomes will be one less, i.e. 77. The designations of the sex chromosomes of the rooster and the sperm it produces will remain the same, and the diploid number of chromosomes in the rooster is one more than in the chicken.
The diploid number of chromosomes in butterflies, including silkworms (see Chapter IV) is 56.
Let's talk about how many chromosomes a rooster and chicken have. Like mammals, the cells of these birds have a female or male chromosome set. Scientists have long argued that it is impossible to determine the sex of a chicken embryo until a certain point in development. But with the help of laboratory research it was possible to find out that this is not so. The cells of the embryo store information about gender from the third week of formation.
About hens and roosters
Chickens are one of the most common inhabitants of farms. In favorable conditions they can live 12-15 years. But in practice this rarely happens. The bird is slaughtered after 2-3 years of life, when its egg production drops. At large poultry farms, chickens are sent to slaughter a year after the first laying.
The average weight of a female is 3.5 kg, and egg production is 120 eggs per year. But performance depends on the breed and conditions of detention. Find out more in the article “What kind of bird is a domestic chicken.”
The rooster is the owner of the chicken coop and is famous for his wayward character and courage. He is the main instigator of fights in the herd. Therefore, only one rooster should live in a chicken family. Otherwise there will always be conflicts.
For each male there are about 10 hens. If there are more of them, problems with health and productivity will begin.
The main differences between males and females:
- a long tail;
- large earrings;
- luxurious bright plumage.
The pride of the cockerels is their fleshy scarlet comb. Details in the article “What a rooster should look like: description of the bird.”
Let's talk about chromosomes
Where are they located?
These are nucleoprotein structures located in the cells of the body of birds. They are carriers of genetic information and consist of spiral-shaped DNA molecules and proteins.
The complete chromosome set of chickens is called a karyotype. It includes information about the shape, size and abundance of genetic material.
All living organisms have chromosomes. But each bird has its own set. It is constant and does not change with age.
Externally, the structures look like a long thread. There are many beads on it - genes. Each gene occupies a specific place - a locus.
What are they responsible for?
Genes never move along a chromosome. Their task is to manage the characteristics of an individual.
Chromosomes are involved in storing and transmitting accumulated information from mother to offspring.
After numerous studies, scientists have determined how many chromosomes a chicken and a rooster have - 78. This is a fairly large number compared to other mammals. For example, people have only 46 of them.
During evolution, chickens and roosters have suffered the least amount of genetic changes compared to other birds.
What determines the sex of birds
Only healthy roosters or chickens have 78 chromosomes. If during the formation of eggs the female begins to have problems with the development of the embryo, their number may change.
Chickens have an XY set of chromosomes, and roosters have an XX set. In many mammals, including humans, the opposite is true.
Scientists from the UK conducted a study of healthy chicken embryos. It turned out that less than a day after fertilization, the sex of the embryo is determined.
In other mammals, this occurs only after the formation of the reproductive glands. This fact was determined by the production of RNA molecules.
For detailed instructions on determining the sex of a chicken before hatching, see the article How to Tell the Sex of a Chicken by Its Egg.
To find out the sex after hatching, read the article “Rooster or hen: how to determine the sex of a chicken.”
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From school biology textbooks, everyone has become familiar with the term chromosome. The concept was proposed by Waldeyer in 1888. It literally translates as painted body. The first object of research was the fruit fly.
General information about animal chromosomes
A chromosome is a structure in the cell nucleus that stores hereditary information. They are formed from a DNA molecule that contains many genes. In other words, a chromosome is a DNA molecule. Its amount varies among different animals. So, for example, a cat has 38, and a cow has 120. Interestingly, earthworms and ants have the smallest numbers. Their number is two chromosomes, and the male of the latter has one.
In higher animals, as well as in humans, the last pair is represented by XY sex chromosomes in males and XX in females. It should be noted that the number of these molecules is constant for all animals, but their number differs in each species. For example, we can consider the content of chromosomes in some organisms: chimpanzees - 48, crayfish - 196, wolves - 78, hare - 48. This is due to the different level of organization of a particular animal.
On a note! Chromosomes are always arranged in pairs. Geneticists claim that these molecules are the elusive and invisible carriers of heredity. Each chromosome contains many genes. Some believe that the more of these molecules, the more developed the animal, and the more complex its body is. In this case, a person should have not 46 chromosomes, but more than any other animal.
How many chromosomes do different animals have?
You need to pay attention! In monkeys, the number of chromosomes is close to that of humans. But the results are different for each species. So, different monkeys have the following number of chromosomes:
- Lemurs have 44-46 DNA molecules in their arsenal;
- Chimpanzees – 48;
- Baboons – 42,
- Monkeys – 54;
- Gibbons – 44;
- Gorillas – 48;
- Orangutan – 48;
- Macaques - 42.
The canine family (carnivorous mammals) has more chromosomes than monkeys.
- So, the wolf has 78,
- the coyote has 78,
- the small fox has 76,
- but the ordinary one has 34.
- The predatory animals lion and tiger have 38 chromosomes.
- The cat's pet has 38, while his dog opponent has almost twice as much - 78.
In mammals that are of economic importance, the number of these molecules is as follows:
- rabbit – 44,
- cow – 60,
- horse – 64,
- pig – 38.
Informative! Hamsters have the largest chromosome sets among animals. They have 92 in their arsenal. Also in this row are hedgehogs. They have 88-90 chromosomes. And kangaroos have the smallest amount of these molecules. Their number is 12. A very interesting fact is that the mammoth has 58 chromosomes. Samples were taken from frozen tissue.
For greater clarity and convenience, data from other animals will be presented in the summary.
Name of animal and number of chromosomes:
| Spotted martens | 12 |
| Kangaroo | 12 |
| Yellow marsupial mouse | 14 |
| Marsupial anteater | 14 |
| Common opossum | 22 |
| Opossum | 22 |
| Mink | 30 |
| American badger | 32 |
| Corsac (steppe fox) | 36 |
| Tibetan fox | 36 |
| Small panda | 36 |
| Cat | 38 |
| a lion | 38 |
| Tiger | 38 |
| Raccoon | 38 |
| Canadian beaver | 40 |
| Hyenas | 40 |
| House mouse | 40 |
| Baboons | 42 |
| Rats | 42 |
| Dolphin | 44 |
| Rabbits | 44 |
| Human | 46 |
| Hare | 48 |
| Gorilla | 48 |
| American fox | 50 |
| striped skunk | 50 |
| Sheep | 54 |
| Elephant (Asian, savannah) | 56 |
| Cow | 60 |
| Domestic goat | 60 |
| Woolly monkey | 62 |
| Donkey | 62 |
| Giraffe | 62 |
| Mule (hybrid of a donkey and a mare) | 63 |
| Chinchilla | 64 |
| Horse | 64 |
| Gray fox | 66 |
| White-tailed deer | 70 |
| Paraguayan fox | 74 |
| Small fox | 76 |
| Wolf (red, ginger, maned) | 78 |
| Dingo | 78 |
| Coyote | 78 |
| Dog | 78 |
| Common jackal | 78 |
| Chicken | 78 |
| Pigeon | 80 |
| Turkey | 82 |
| Ecuadorian hamster | 92 |
| Common lemur | 44-60 |
| Arctic fox | 48-50 |
| Echidna | 63-64 |
| Jerzy | 88-90 |
Number of chromosomes in different animal species
As you can see, each animal has a different number of chromosomes. Even among representatives of the same family, indicators differ. We can look at the example of primates:
- the gorilla has 48,
- the macaque has 42, and the marmoset has 54 chromosomes.
Why this is so remains a mystery.
How many chromosomes do plants have?
Plant name and number of chromosomes:
Video
1 . Unlike DNA molecules, protein molecules contain atoms:
a) sulfur;
b) hydrogen;
c) nitrogen;
d) protein and DNA molecules contain the same atoms.
2 . Mutations occur as a result of changes in:
a) DNA;
b) cellular structures;
c) metabolism;
d) squirrel.
3 . If you take ribosomes and enzymes from bacteria, ATP and ADP and amino acids from a fungus, and DNA from a lizard for protein synthesis, then the following proteins will be synthesized:
a) mushroom;
b) lizards;
c) bacteria;
d) all three organisms.
4 . A living system corresponding to the biomolecular level of organization of living matter:
a) plant chloroplast;
b) egg of a mammal;
c) influenza virus;
d) there are no such living systems on Earth at all.
5 . A chemical element that is an essential component of the hemoglobin protein in mammals:
a) zinc;
b) copper;
c) chlorine;
d) iron.
6 . To quickly restore performance when tired during preparation for an exam, it is better to eat:
a) apple;
b) a piece of sugar;
c) sandwich;
d) a piece of meat.
7 . A plant cell, unlike an animal cell, contains:
a) ribosomes;
b) vacuoles, plastids and cellulose membrane;
c) reserve nutrients;
d) more chromosomes in the nucleus.
8 . All of the following organisms are prokaryotes:
a) bacteria, yeast, blue-green algae;
b) bacteria, blue-green algae;
c) yeast, bacteria;
d) viruses and bacteria.
9 . All of the following organisms have cell nuclei:
a) parrot, fly agaric, birch;
b) cat, nitrogen-fixing bacteria;
c) Escherichia coli, roundworm;
d) roundworm, AIDS virus, octopus.
10 . Of the listed cells, there are more mitochondria in:
a) bird eggs;
b) erythrocytes of mammals;
c) mammalian spermatozoa;
d) green plant cells.
11 . Chemical reactions of anabolism predominate in cells:
a) plants;
b) mushrooms;
c) animals;
d) the level of anabolism is the same for everyone.
12 . The following cells take part in sexual reproduction in multicellular organisms:
a) disputes;
b) eggs and sperm;
c) somatic;
d) various, depending on the circumstances.
13 . The cell cycle is:
a) the totality and order of all chemical reactions in the cell;
b) the life of a cell from division to division;
c) the life of a cell from division to division plus the time of division itself;
d) the time when the cell prepares to divide.
14 . Before entering the mitosis stage, a somatic cell of a diploid organism has a set of chromosomes:
a) diploid (2 n);
b) haploid ( n);
c) tetraploid (4 n);
d) depending on the circumstances.
15 . The set of chromosomes is haploid in:
a) a chicken egg;
b) wheat seed cells;
c) human leukocytes;
d) integumentary cells of higher plants.
16 . Reproduction methods typical only for plants:
a) seeds, tendrils, spores;
b) bulb, mustache, layering;
c) seeds, layering, spores;
d) cell division, bulb, whiskers.
17 . Advantages of sexual reproduction compared to asexual reproduction:
a) the simplicity of the process;
b) the complexity of the process;
c) in greater genetic diversity of individuals of the next generation;
d) in accelerating the growth of species numbers.
18 . The stage of meiosis and the reason why mutations can occur in the germ cell:
a) as a result of crossing over in prophase I;
b) as a result of incorrect chromosome segregation in telophase I or II;
c) as a result of radioactive irradiation of the body during the formation of germ cells;
d) for any of the above reasons.
19 . A group of living systems representing the organismic level of organization:
a) apple tree, apple, codling moth caterpillar;
b) apple tree, earthworm, apple flower;
c) apple tree, earthworm, caterpillar;
d) apple, caterpillar, earthworm.
20 . The correct sequence of the initial stages of ontogenesis:
a) zygote, gastrula, blastula;
b) fertilization, gastrula, blastula;
c) gametogenesis, fertilization, blastula, gastrula;
d) none of the answers are correct.
21 . Fertilization in the female body in humans normally occurs:
a) in the uterus;
b) in the upper part of the fallopian tubes;
c) in the vagina;
d) in the ovaries.
22 . To conceive two identical twins, fertilization is necessary:
a) one egg with two sperm;
b) two eggs with one sperm;
c) two eggs with two sperm;
d) one egg with one sperm.
23 . More heterozygous individuals will be obtained from crossing:
A) AABB ґ aaBB;
b) ААbb ґ aaBB;
V) AaBb ґ AaBb;
G) aabb ґ Aabb.
24 . The normal set of sex chromosomes in a rooster is:
a) XO;
b) XXY;
c) XX;
d) XY.
25 . If parents have blood types I and IV, then children may have blood types:
a) only I;
b) IV only;
c) only II or III;
d) only I or IV.
26 . For the first time he discovered and described the fundamental laws of gene distribution in offspring when crossing hybrids:
a) J.-B. Lamarck;
b) G. Mendel;
c) C. Darwin;
d) N.I. Vavilov.
27 . The unit of evolution is:
a) individual;
b) type;
c) population;
d) ecosystem.
28 . An example of non-hereditary variability is:
a) the appearance of an albino in the offspring of a pride of lions;
b) an increase in the percentage of milk fat in cows with changes in the composition and feeding regimen;
c) increasing the percentage of milk fat in cows of a highly productive breed;
d) loss of vision in the mole as a result of evolution.
29 . The factor determining the direction of evolution is:
a) isolation;
b) mutation;
c) natural selection;
d) fluctuations in population numbers.
30 . An example of aromorphosis is:
a) the appearance of pulmonary respiration in amphibians;
b) flat body shape in bottom-dwelling fish;
c) lack of color in cave animals;
d) the presence of thorns and prickles in plant fruits.
31 . The presence of microbes in the environment around the body is:
a) abiotic environmental factor;
b) biotic environmental factor;
c) anthropogenic factor;
d) limiting factor.
32. An example of biogeocenosis is:
a) a pond with all its inhabitants;
b) aquarium;
c) all living inhabitants of the pond;
d) all representatives of the pond flora.
33. A brown bear in a natural ecosystem acts as a third-order consumer when it eats:
a) berries;
b) pike;
c) wild boar;
d) bulbs of herbaceous plants.
34 . The signal for the start of migration in migratory birds is:
a) the onset of cold weather;
b) age of the chicks;
c) change in day length;
d) lack of food.
35 . An integral component of all natural ecosystems are:
a) fungi and bacteria;
b) herbivores;
c) carnivores;
d) insects.
36 . In the food chain grass – grasshoppers – lizards – owls For a pair of owls with a total weight of 5 kg to exist, the following grass is needed:
a) 50 t;
b) 5 t;
c) 500 kg;
d) 2.5 t.
37 . Indicate between which species competitive relationships may arise:
a) man and cockroaches;
b) hawk and wolf;
c) elk and mouse;
d) mustang and bison.
38 . The relationship between humans and E. coli is an example:
39. The gas function of living matter on Earth is carried out by:
a) only plants;
b) plants and some bacteria;
c) plants, bacteria and animals;
d) all living beings.
40. “There is no chemical force on the earth’s surface more constantly active, and therefore more powerful in its ultimate effects, than living organisms taken as a whole.” These words belong to:
a) N.I. Vavilov;
b) V.I. Vernadsky;
c) D.I. Mendeleev;
d) K.E. Tsiolkovsky.
Answers.
1 - A. 2 - A. 3 – b. 4 - V. 5 - G. 6 – b. 7 – b. 8 – b. 9 - A. 10 - V. 11 - A. 12 – b. 13 - V. 14 - A. 15 - A. 16 – b. 17 - V. 18 - G. 19 - V. 20 - G. 21 – b. 22 - G. 23 – b. 24 - V. 25 - V. 26 – b. 27 - V. 28 – b. 29 - V. 30 - A. 31 – b. 32 - A. 33 – b. 34 - V. 35 - A. 36 – b. 37 - G. 38 - G. 39 - G. 40 – b.
Selected tasks from the examination paper in biology for the 11th grade