Professor of Genetics Darren Griffin and professor of molecular biology and reproduction Peter Ellis from the University of Kent in his new book told that the Y-chromosome, due to which the appearance of men, is waiting for the inevitable complete degradation.

Degeneration of the Y-chromosome is already underway. And if the case continues at the same pace, it will disappear in 4.6 million years. This may sound like a long time, unless you recall the age of the Earth - 3.5 billion years, the authors write in an article on Science Alert.

Y-chromosome was not always such. If we rewind time 166 million years ago, to the very first mammals, we will see a completely different picture. The early "proto-Y-chromosome" was initially the same size as the X chromosome, and contained all the same genes.

However, Y-chromosomes have a fundamental drawback. Unlike all the other chromosomes that are available in two copies in each of the cells, the Y-chromosome is present as a single copy transmitted from the fathers to their sons.

This means that genes on the Y chromosome can not be subjected to genetic recombination, "shuffling" genes that occur in each generation, which helps to eliminate damaging mutations.

Deprived of the benefits of recombination, Y-chromosomal genes degenerate over time and eventually are lost from the genome.

Despite this, recent studies have shown that the Y chromosome has developed some fairly effective mechanisms that slow the rate of gene loss.

For example, during a recent Danish study published in PLoS Genetics, fragments of the Y chromosome were sequenced in 62 different men. Scientists have found that it is subject to large-scale structural rearrangements that allow for "gene amplification" - to obtain multiple copies of genes, which contributes to the health of spermatozoa and reduces the risk of gene loss.

The study also showed that the Y chromosome has developed unusual structures called "palindromes" (DNA sequences that are read equally, from which end, or a crook, like the word "stamping") that protect it from further degradation.

In relation to the question of whether the Y chromosome will disappear altogether, the scientific community is divided into two halves. The first believes that the protective mechanisms perform great work and eventually save the Y chromosome. The second is convinced that these measures can only delay the inevitable disappearance of the male chromosome.

The authors of the book note that, even if the Y-chromosome ceases to exist, this does not necessarily mean that males (and men) will disappear. Even in species that completely lost their Y-chromosomes, males and females are still required for reproduction.

In these cases, the gene - "sex switch" SRY, located on Y, moved to another chromosome. However, a new chromosome that determines sex again begins the process of degeneration because of the same lack of recombination suffered by the doomed Y chromosome.

Source: My planet.