The y chromosome disappears-so what happens to men?

The y chromosome disappears-so what happens to men?

Darren Griffin, University of Kent and Peter Ellis, University of Kent

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The Y chromosome may be a symbol of masculinity, but it becomes increasingly clear that it is anything but strong and stable. Although it carries the "master switch" gene Sry, which determines whether an embryo develops as a man (XY) or woman (XX), it contains very few other genes and is the only chromosome that is not necessary for life. After all, women also get along quite well.

In addition, the Y chromosome is quickly degenerated, so that women have two completely normal X chromosomes, but men only one. This may sound like a long time, but it is not when you consider that there have been living on Earth for 3.5 billion years.

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The Y chromosome was not always like that. If we turn the clock back to the time 166 million years ago, to the very first mammals, the story looks completely different. The early "Proto-Y" chromosome originally had the same size as X chromosome and contained the same genes. However, Y chromosomes have a fundamental mistake. In contrast to all other chromosomes, of which we have two copies in each of our cells, y chromosomes are only available in one copy and are passed on by the father to the son.

This means that genes cannot be subjected to a genetic recombination on the Y chromosome, the "mixing" of genes that takes place in every generation and helps to eliminate harmful gene mutations. Without the advantages of recombination, y-chromosomal genes degenerate over time and finally lose from the genome.

Chromosom Y in red, next to the much larger X-chromosome. National Institute for Human Research

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Nevertheless, recent research has shown that the Y-chromosome has developed some rather convincing mechanisms to "step on the brakes" and to slow down the loss of gene so far that it may come to a standstill.

In a Danish study recently published in PLOS Genetics, parts of the Y chromosome of 62 different men, for example, were sequenced and found that it tends to achieve large-scale structural surroundings that enable "genamplification"-the acquisition of several copies of genes that promote health function and alleviate genetic loss. id = "ezoic-pub-ad-placeholder-690" Class = "Ezoic-adpicker-ad"> @Media (Min-Width: 0PX) {#Div-Gpt-Ad-Healthy_holistic_Living_Com-Large-Leader Board-2-0-Asloaded {Max-Width: 336px! Important; Max-Height: 280px! Important;}}

The study also showed that the Y-chromosome developed unusual structures that are called "Palindrome" (DNA sequences that read forward and backwards-like the word "kayak") that protect it from further breakdown. They recorded a high rate of "genetic conversion events" within the palindromic sequences on the Y chromosome-this is basically a "copying and inserting" process that enables damaged genes to be repaired as a template using an undamaged security.

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With a view to other species (y chromosomes are available in mammals and some other species), there are more and more indications that the Y chromosome gene amplification is a general principle. These reinforced genes play a crucial role in sperm production and (at least in rodents) in regulating the gender ratio of the offspring. Recently, researchers in Molecular Biology and Evolution have proven that this increase in the number of genes is a result of natural selection in mice.

When it comes to the question of whether the Y chromosome will actually disappear, the scientific community, like Great Britain, is divided into the "Leavers" and the "Remainers". The latter group argues that their defense mechanisms do an excellent job and saved the Y chromosome. But the losers say that they only allow y chromosome to hold onto their fingernails before it finally falls off the cliff. The debate therefore continues.

A leading supporter of the Leave-Argumente, Jenny Graves from La Trobe University in Australia, claims that the Y chromosomes, if you take a long-term perspective, are inevitably consecrated to doom-even if they sometimes last a little longer than expected. In a work from 2016, she points out that Japanese spiked rats and mole rattles have completely lost their y chromosomes-and argues that the process of loss or the development of genes inevitably leads to fertility problems on the Y-chromosoma. This in turn can ultimately push the formation of completely new species.

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the downfall of men?

As we argue in a chapter of a new e-book, the disappearance of the Y chromosome does not necessarily mean that the men themselves are on their way there. Even with the species that have actually completely lost their y chromosomes, both males and females are necessary for reproduction.

The interesting thing about humans, however, is that although the Y chromosome is needed for normal human reproduction, many of the genes it carries it are not necessary if they apply techniques of assisted reproduction. This means that genetic engineering could soon be able to replace the gene function of the Y chromosome and to give same-sex couples or sterile men the opportunity to get pregnant. But even if it were possible for everyone to become pregnant in this way, it would be extremely unlikely that fertile people would simply stop continuing in a natural way.

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Although this is an interesting and hotly discussed area of ​​gene research, there is no need to worry. We don't even know whether the Y chromosome will disappear at all. And even if this is the case, as we have shown, we will most likely continue to need men so that normal reproduction can continue.

In fact, the view of a "farm animal"-like system, in which a few "happy" men are selected to testify the majority of our children, certainly not in sight. In any case, there will be far more urgent concerns in the next 4.6 million years.

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Darren Griffin, Professor of Genetics, University of Kent and Peter Ellis, lecturer for molecular biology and reproduction, University of Kent

This article was again published by The Conversation under a Creative Commons license. Read the original article.

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