Why men die before women? Case in chromosomes

Men on average die before women. For example, in Russia the difference in life expectancy between the sexes is almost ten years. What prevents men to live as long as their wonderful friend and companion?

a Popular hypothesis States that men drink more alcohol, smoke more often, are more willing to risk and less likely to seek medical attention in case of sickness. At least some of these theses are confirmed by scientists, and there is no doubt that such factors do affect the life expectancy of a strong half of mankind.

However, there is a more fundamental reason for lurking at the DNA level. This convinces the scientific article published in the journal Biology Letters.

the Authors tested the hypothesis unprotected X chromosome. It is as follows.

As you know, all asexual chromosomes in humans come in pairs. That is, every part of their structure a gene is present in DNA in two copies: one for each chromosome. Thus, genes have variants (alleles), some of which are harmful, shortening the life.

If the same gene on different chromosomes are represented by different alleles, which of them will ultimately work? There are a lot of options. But, if one allele is recessive (“weak”), its impact on the body completely or partially suppresses the other allele in the pair. Therefore, the “healthy” allele suppresses often “sick” (if recessive), saving the wearer from a genetic disorder.

(in Fact, the danger of incest is that relatives often the same harmful recessive alleles, which leads to tragic consequences for their children).

But what about sex chromosomes? In women they are also paired: they have two X chromosomes. But in men it is one of the sex chromosomes — X and the other U.

the Y-chromosome is several times shorter than the X chromosome: first, about 80 genes, while the second more 1400. In addition, certain genes of the Y-chromosome are only present in it (and men do men).

All this leads to the fact that the stronger sex the vast majority of genes the X chromosome has no pair. This means that some features of the organism are determined by only one allele for the absence of his “partner”. And if this allele carries a harmful mutation, it will influence nothing kompensiruet. It is natural to assume that such incidents can shorten the life of the men.

note that in this mechanism there is nothing specifically human. He must act on any species in which one of the sexes is unpaired sex chromosomes, and one of them is shorter than the other. By the way, not all animals that dubious pleasure fell to the share of males. Birds, butterflies and moths all on the contrary: unpaired sex chromosomes are female.

the Authors compared life expectancy of males and females in many species.Photo Pixabay.

the Hypothesis of unprotected X chromosome were expressed many decades ago. Since then, she several times checked, but usually these studies are limited to one or more types.

the authors of the new work approached the issue of scale. They performed an impressive meta-analysis of scientific literature, gathering information about 229 species belonging to 99 families, 38 orders and eight classes (!).

“We looked at the data on life expectancy not only primates, other mammals and birds, but also reptiles, fish, amphibians, arachnids, cockroaches, grasshoppers, beetles, butterflies and moths”, lists the first author Zoe Xirocostas (Zoe Xirocostas).

it Turned out that for all this diversity of living beings is true the General rule: the carriers of the unpaired sex chromosomes (either males or females) to die before. The average life expectancy differs by 17.6%.

But also revealed an unexpected circumstance. Males “chromosomal inequality” gave way stronger than females. So, species that have unpaired sex chromosomes are males, females are living longer (average all types) by 20.9%. At the same time, among animals that have unpaired chromosomes have females, males live only 7.1% longer.

there is Probably a reason why males have a lower tolerance “chromosomal helplessness”. And it is unlikely in the case of spiders or frogs it is associated with alcohol and tobacco.

Perhaps, say the authors, but males have a “defective” chromosome more different from his “partner” and therefore less “covers” of her genes. In addition, it may be the intricacies of the telomere. Finally, biologists do not exclude that the reason of the side effects of sexual selection.

the researchers also hypothesized that the difference in life expectancy between the sexes is proportional to the difference in the length of the chromosomes. Check it will help future research.

By the way, earlier “Conduct.Science” (nauka.vesti.ru) wrote about how biologists in search of the secrets of longevity analyzed the world’s largest family tree.

Text: To.Science