We also know from the school biology course thatin the normal formation of the human body (read: without various congenital abnormalities), most of our genetic information is encoded in 23 pairs of chromosomes. But have you ever wondered why these pairs are exactly 23? Why not 24, 25 or even 16? And in general, why are chromosomes an even number? Let's figure it out.
DNA and chromosomes
To understand what chromosomes are, you first need tounderstand what DNA is. DNA is a complex molecule found in all plants and animals. It is contained in almost every cell of the body and carries all the information necessary to maintain the vital functions of the body, ensure all internal processes and, most importantly, reproduce. DNA is the main method of transmitting hereditary information and in the process of reproduction part of the DNA is transferred from both parents to the offspring.
See also: CRISPR helped to create a new species with one giant chromosome
Such a huge amount of information thatcarries our DNA, should take quite a lot of "space". And indeed it is. If you "stretch" the DNA contained in just one cell, then its length will be about 2 meters. And our body has a rather clever packaging system for all this data. And the chromosome helps with it.
Why exactly 23 pairs of chromosomes
Immediately it is worth noting that the number of 23 pairsThe chromosome is not universal among sentient beings. First, humans are “diploid” species, which means that the majority of our chromosomes form matched pairs (although there are also species that have an odd number of chromosomes). This simplifies the storage of information. However, the complexity of the organization of the species does not depend on the number of pairs of chromosomes. So, for example, some types of frogs have 18 pairs of chromosomes, and shrimps have 90 pairs!
Who would have thought, but this tiny species has more chromosome pairs than humans
"People have 23 pairs of chromosomes, whilegreat apes (chimpanzees, gorillas, and orangutans) have 24 pairs of chromosomes, ”says Belen Hurl, a researcher at the National Research Institute for the Human Genome. “This is due to the fact that in the evolutionary line of man the two chromosomes of the ancestors of the monkey merged into one. Thus, a person has one less chromosome pair. This is one of the main differences between the human genome and the genome of our closest relatives. It can be said that this quantity is historically conditioned. At the same time, it cannot be denied that the number of chromosomes in the distant ancestors was different, but such a set of genes did not allow them to exist normally and therefore the organisms "had to" change. "
What happens if the number of chromosomes changes
Increase or decrease in the number of chromosomes inthe adult organism can hardly happen. But this can happen during the formation of the fetus in the womb. One of the most common forms of chromosome pathology is trisomy, which consists in the presence of an additional chromosome in the cells. One of the well-known results of trisomy is Down syndrome, which is a condition caused by the presence of three (and not two) chromosomes in 21 pairs. The loss of one chromosome in a cell is called monosomy and describes a condition in which people have only one copy of a certain chromosome per cell, not two.
An odd number of chromosomes makes it harderthe process of reading information or disrupts the operation of some systems (for example, the absence of sex chromosomes in a number of congenital diseases does not allow progeny). Thus, the historically formed number of 23 pairs of chromosomes allows us to live on this planet and preserve the integrity of our species.
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