How many chromosomes does a caterpillar have? How many chromosomes do different animals have?

MOSCOW, July 4— RIA Novosti, Anna Urmantseva. Who has the larger genome? As you know, some creatures have a more complex structure than others, and since everything is written in DNA, then this should also be reflected in its code. It turns out that a person with his developed speech must be more complex than a small round worm. However, if you compare us with a worm in terms of the number of genes, you get about the same thing: 20 thousand genes of Caenorhabditis elegans versus 20-25 thousand of Homo sapiens.

Even more offensive for the “crown of earthly creatures” and the “king of nature” are comparisons with rice and corn - 50 thousand genes in relation to human 25.

However, maybe we think wrong? Genes are “boxes” in which nucleotides are packaged—the “letters” of the genome. Maybe count them? Humans have 3.2 billion nucleotide pairs. But the Japanese crow's eye (Paris japonica) - a beautiful plant with white flowers - has 150 billion base pairs in its genome. It turns out that a person should be 50 times simpler than some flower.

And the lungfish protoptera (lungfish - having both gill and pulmonary respiration) turns out to be 40 times more complex than humans. Maybe all fish are somehow more complex than people? No. The poisonous fugu fish, from which the Japanese prepare a delicacy, has a genome eight times smaller than that of humans and 330 times smaller than that of the lungfish Protoptera.
All that remains is to count the chromosomes - but this confuses the picture even more. How can a person be equal in number of chromosomes to an ash tree, and a chimpanzee to a cockroach?

Evolutionary biologists and geneticists encountered these paradoxes a long time ago. They were forced to admit that the size of the genome, no matter how we try to calculate it, is strikingly unrelated to the complexity of the organization of organisms. This paradox was called the “C-value mystery,” where C is the amount of DNA in the cell (C-value paradox, the exact translation is “genome size paradox”). And yet some correlations between species and kingdoms exist.

© Illustration by RIA Novosti. A. Polyanina

© Illustration by RIA Novosti. A. Polyanina

It is clear, for example, that eukaryotes (living organisms whose cells contain a nucleus) have, on average, larger genomes than prokaryotes (living organisms whose cells do not contain a nucleus). Vertebrates have, on average, larger genomes than invertebrates. However, there are exceptions that no one has yet been able to explain.

There have been suggestions that genome size is related to the length of an organism's life cycle. Using plants as an example, some scientists have argued that perennial species have larger genomes than annuals, usually with a difference of several times. And the smallest genomes belong to ephemeral plants, which go through the full cycle from birth to death within a few weeks. This issue is currently being actively discussed in scientific circles.

Explains the leading researcher at the Institute of General Genetics. N.I. Vavilova of the Russian Academy of Sciences, Professor of the Texas Agromechanical University and the University of Gottingen Konstantin Krutovsky: “The size of the genome is not related to the duration of the life cycle of the organism! For example, there are species within the same genus that have the same genome size, but may differ in life expectancy tens, if not hundreds of times. In general, there is a connection between genome size and evolutionary advancement and complexity of organization, but with many exceptions. Generally, genome size is associated with ploidy (copy number) of the genome (and polyploids are found in both plants and animals) and amount of highly repetitive DNA (simple and complex repeats, transposons and other mobile elements)."

There are also scientists who have a different point of view on this issue.

Recent genetic studies of dolphins suggest that the ancestors of animals are ungulates. These are their closest relatives. The answer to the question about how many chromosomes do dolphins have, suggests a hypothesis about the primary habitation of these mammals on land.

How many chromosomes do dolphins have?

Chromosomes are a special structure that makes up DNA. It is located in the nucleus of the body's cell. The task of the chromosome is to store information about the structure of the body, its individual characteristics and gender. The dolphin has 44 chromosomes. Since they are located in double numbers in the cells, there are 22 pairs in total. A certain set of chromosomes establishes the karyotype of any representative of the animal or plant world.

Number of chromosomes in other sea inhabitants:

1. Penguin - 46.
2. Blue whale – 44.
3. Sea urchin – 42.
4. Shark – 36.
5. Seal – 34.

Dolphins belong to the species of cetaceans, the subspecies being toothed whales (dolphins, sperm whales, killer whales). There are about 50 species of dolphins in total. They primarily live in seawater, but there are a few species that live in large rivers. Dolphins, like land animals, are warm-blooded, viviparous, and feed their young with their milk. They breathe through their lungs; to do this, they emerge from the water several times during the day. A dolphin is completely different from a shark. The sea predator belongs to the class of fish, since it has gills, and its offspring do not feed on milk. The shark simply does not have milk.

Genetic research

Dolphins communicate with us

The existing theory about the origin of man from apes has become less convincing after recent studies of dolphin chromosomes. As it turns out, humans and dolphins have striking similarities in their chromosomal structures. Among other organisms living on earth, the dolphin turned out to be closest to artiodactyls and hippopotamus. Many similarities were found with elephants. Humans, dolphins and elephants are distinguished by the proportional volume of their brain relative to their body. The special structure of the nervous system determines a significant number of synapses (nerve connections) and cerebral convolutions. These properties allow dolphins to learn quickly.

Dolphins have higher intelligence than monkeys. Sea inhabitants recognize themselves in the mirror, understand the intonation of human speech, know how to imitate and strictly follow the rules that have developed in the school. Cetaceans communicate using low-frequency sounds. Sea water contains magnesium sulfate, which absorbs high-frequency noise. Therefore, the inhabitants of the sea have learned to use sounds that can travel long distances in water.

The human genes responsible for sleep are simply modified in dolphins. Therefore, these mammals sleep in a special way. During the research, scientists discovered DNA that is responsible for keeping one half of the brain awake while the other is asleep. This happened during the process of mutation. Scientists have concluded that after humans, dolphins have the highest intelligence on the planet.

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 many - 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:

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

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B chromosomes have not yet been discovered in humans. But sometimes an additional set of chromosomes appears in cells - then they talk about polyploidy, and if their number is not a multiple of 23 - about aneuploidy. Polyploidy occurs in certain types of cells and contributes to their increased work, while aneuploidy usually indicates disturbances in the functioning of the cell and often leads to its death.

We must share honestly

Most often, an incorrect number of chromosomes is a consequence of unsuccessful cell division. In somatic cells, after DNA duplication, the maternal chromosome and its copy are linked together by cohesin proteins. Then kinetochore protein complexes sit on their central parts, to which microtubules are later attached. When dividing along microtubules, kinetochores move to different poles of the cell and pull chromosomes with them. If the crosslinks between copies of a chromosome are destroyed ahead of time, then microtubules from the same pole can attach to them, and then one of the daughter cells will receive an extra chromosome, and the second will remain deprived.

Meiosis also often goes wrong. The problem is that the structure of linked two pairs of homologous chromosomes can twist in space or separate in the wrong places. The result will again be an uneven distribution of chromosomes. Sometimes the reproductive cell manages to track this so as not to pass the defect on to inheritance. The extra chromosomes are often misfolded or broken, which triggers the death program. For example, among spermatozoa there is such selection for quality. But the eggs are not so lucky. All of them are formed in humans even before birth, prepare for division, and then freeze. The chromosomes have already been duplicated, tetrads have been formed, and division has been delayed. They live in this form until the reproductive period. Then the eggs mature in turn, divide for the first time and freeze again. The second division occurs immediately after fertilization. And at this stage it is already difficult to control the quality of division. And the risks are greater, because the four chromosomes in the egg remain cross-linked for decades. During this time, damage accumulates in cohesins, and chromosomes can spontaneously separate. Therefore, the older the woman, the greater the likelihood of incorrect chromosome segregation in the egg.

Aneuploidy in germ cells inevitably leads to aneuploidy of the embryo. If a healthy egg with 23 chromosomes is fertilized by a sperm with extra or missing chromosomes (or vice versa), the number of chromosomes in the zygote will obviously be different from 46. But even if the sex cells are healthy, this does not guarantee healthy development. In the first days after fertilization, embryonic cells actively divide in order to quickly gain cell mass. Apparently, during rapid divisions there is no time to check the correctness of chromosome segregation, so aneuploid cells can arise. And if an error occurs, then the further fate of the embryo depends on the division in which it happened. If the balance is disturbed already in the first division of the zygote, then the entire organism will grow aneuploid. If the problem arose later, then the outcome is determined by the ratio of healthy and abnormal cells.

Some of the latter may continue to die, and we will never know about their existence. Or he can take part in the development of the organism, and then it will turn out mosaic- different cells will carry different genetic material. Mosaicism causes a lot of trouble for prenatal diagnosticians. For example, if there is a risk of having a child with Down syndrome, sometimes one or more cells of the embryo are removed (at a stage when this should not pose a danger) and the chromosomes in them are counted. But if the embryo is mosaic, then this method becomes not particularly effective.

Third wheel

All cases of aneuploidy are logically divided into two groups: deficiency and excess of chromosomes. The problems that arise with a deficiency are quite expected: minus one chromosome means minus hundreds of genes.

If the homologous chromosome works normally, then the cell can get away with only an insufficient amount of the proteins encoded there. But if some of the genes remaining on the homologous chromosome do not work, then the corresponding proteins will not appear in the cell at all.

In the case of an excess of chromosomes, everything is not so obvious. There are more genes, but here - alas - more does not mean better.

Firstly, excess genetic material increases the load on the nucleus: an additional strand of DNA must be placed in the nucleus and served by information reading systems.

Scientists have discovered that in people with Down syndrome, whose cells carry an extra 21st chromosome, the functioning of genes located on other chromosomes is mainly disrupted. Apparently, an excess of DNA in the nucleus leads to the fact that there are not enough proteins to support the functioning of chromosomes for everyone.

Secondly, the balance in the amount of cellular proteins is disrupted. For example, if activator proteins and inhibitor proteins are responsible for some process in a cell, and their ratio usually depends on external signals, then an additional dose of one or the other will cause the cell to stop responding adequately to the external signal. Finally, an aneuploid cell has an increased chance of dying. When DNA is duplicated before division, errors inevitably occur, and the cellular repair system proteins recognize them, repair them, and start doubling again. If there are too many chromosomes, then there are not enough proteins, errors accumulate and apoptosis is triggered - programmed cell death. But even if the cell does not die and divides, then the result of such division will also most likely be aneuploids.

You will live

If even within one cell aneuploidy is fraught with malfunctions and death, then it is not surprising that it is not easy for an entire aneuploid organism to survive. At the moment, only three autosomes are known - 13, 18 and 21, trisomy for which (that is, an extra third chromosome in cells) is somehow compatible with life. This is likely due to the fact that they are the smallest and carry the fewest genes. At the same time, children with trisomy on the 13th (Patau syndrome) and 18th (Edwards syndrome) chromosomes live at best up to 10 years, and more often live less than a year. And only trisomy on the smallest chromosome in the genome, the 21st chromosome, known as Down syndrome, allows you to live up to 60 years.

People with general polyploidy are very rare. Normally, polyploid cells (carrying not two, but from four to 128 sets of chromosomes) can be found in the human body, for example, in the liver or red bone marrow. These are usually large cells with enhanced protein synthesis that do not require active division.

An additional set of chromosomes complicates the task of their distribution among daughter cells, so polyploid embryos, as a rule, do not survive. Nevertheless, about 10 cases have been described in which children with 92 chromosomes (tetraploids) were born and lived from several hours to several years. However, as in the case of other chromosomal abnormalities, they lagged behind in development, including mental development. However, many people with genetic abnormalities come to the aid of mosaicism. If the anomaly has already developed during the fragmentation of the embryo, then a certain number of cells may remain healthy. In such cases, the severity of symptoms decreases and life expectancy increases.

Gender injustices

However, there are also chromosomes, the increase in the number of which is compatible with human life or even goes unnoticed. And these, surprisingly, are sex chromosomes. The reason for this is gender injustice: approximately half of the people in our population (girls) have twice as many X chromosomes as others (boys). At the same time, the X chromosomes not only serve to determine sex, but also carry more than 800 genes (that is, twice as many as the extra 21st chromosome, which causes a lot of trouble for the body). But girls come to the aid of a natural mechanism for eliminating inequality: one of the X chromosomes is inactivated, twists and turns into a Barr body. In most cases, the choice occurs randomly, and in some cells the result is that the maternal X chromosome is active, while in others the paternal one is active. Thus, all girls turn out to be mosaic, because different copies of genes work in different cells. A classic example of such mosaicism is tortoiseshell cats: on their X chromosome there is a gene responsible for melanin (a pigment that determines, among other things, coat color). Different copies work in different cells, so the coloring is spotty and is not inherited, since inactivation occurs randomly.

As a result of inactivation, only one X chromosome always works in human cells. This mechanism allows you to avoid serious troubles with X-trisomy (XXX girls) and Shereshevsky-Turner syndrome (XO girls) or Klinefelter (XXY boys). About one in 400 children is born this way, but vital functions in these cases are usually not significantly impaired, and even infertility does not always occur. It is more difficult for those who have more than three chromosomes. This usually means that the chromosomes did not separate twice during the formation of sex cells. Cases of tetrasomy (ХХХХ, ХХYY, ХХХY, XYYY) and pentasomy (XXXXX, XXXXY, XXXYY, XXYYY, XYYYY) are rare, some of them have been described only a few times in the history of medicine. All of these options are compatible with life, and people often live to an advanced age, with abnormalities manifested in abnormal skeletal development, genital defects, and decreased mental abilities. Typically, the additional Y chromosome itself does not significantly affect the functioning of the body. Many men with the XYY genotype do not even know about their peculiarity. This is due to the fact that the Y chromosome is much smaller than the X and carries almost no genes that affect viability.

Sex chromosomes have another interesting feature. Many mutations of genes located on autosomes lead to abnormalities in the functioning of many tissues and organs. At the same time, most gene mutations on sex chromosomes manifest themselves only in impaired mental activity. It turns out that sex chromosomes largely control brain development. Based on this, some scientists hypothesize that they are responsible for the differences (however, not fully confirmed) between the mental abilities of men and women.

Who benefits from being wrong?

Despite the fact that medicine has been familiar with chromosomal abnormalities for a long time, recently aneuploidy continues to attract the attention of scientists. It turned out that more than 80% of tumor cells contain an unusual number of chromosomes. On the one hand, the reason for this may be the fact that proteins that control the quality of division are able to slow it down. In tumor cells, these same control proteins often mutate, so restrictions on division are lifted and chromosome checking does not work. On the other hand, scientists believe that this may serve as a factor in the selection of tumors for survival. According to this model, tumor cells first become polyploid, and then, as a result of division errors, they lose different chromosomes or parts thereof. This results in a whole population of cells with a wide variety of chromosomal abnormalities. Most are not viable, but some may succeed by chance, for example if they accidentally gain extra copies of genes that trigger division or lose genes that suppress it. However, if the accumulation of errors during division is further stimulated, the cells will not survive. The action of taxol, a common cancer drug, is based on this principle: it causes systemic chromosome nondisjunction in tumor cells, which should trigger their programmed death.

It turns out that each of us may be a carrier of extra chromosomes, at least in individual cells. However, modern science continues to develop strategies to deal with these unwanted passengers. One of them suggests using proteins responsible for the X chromosome and targeting, for example, the extra 21st chromosome of people with Down syndrome. It is reported that this mechanism was brought into action in cell cultures. So, perhaps, in the foreseeable future, dangerous extra chromosomes will be tamed and rendered harmless.

Polina Loseva