The Y chromosome is disappearing, there will be no males in the future?

2021-01-04 | Weird Rokop Original |

Human cells have 23 pairs of chromosomes, 22 of which are autosomes, and another pair are sex chromosomes. The male is XY and the female is XX.

Sex chromosomes determine the difference between men and women. There are about 1,000 genes on the X chromosome, and the Y chromosome is much less than that, only 45.

Whether a baby is male or female before birth depends on whether he or she has a Y chromosome. It can be said that the Y chromosome is the only symbol of male sex.

But now there is a study that shows that with the passage of time, the genes on the Y chromosome are gradually decreasing, which means that it may lose its decisive role in sex.

So, will Y chromosomes really "disappear"? Once they disappear, will human males disappear with them, leaving only females?

Picture: ancient mammals

How do sex chromosomes come from

Actually, sex chromosomes did not exist since ancient times, but were mutated at some point in the evolutionary history of biology, and they were preserved because they were beneficial mutations.

When the first mammals evolved between 10 billion and 200 million years ago, they did not have sex chromosomes, or their sex chromosomes were indistinguishable from autosomes, regardless of size, structure or function.

We can think that these ancient animals don’t need sex chromosomes. How can they distinguish between male and female if they don’t have sex chromosomes?

This question can be answered from existing creatures. For example, the sex of crocodiles is affected by the temperature during incubation, and some cold-blooded vertebrates are hermaphrodite.

At a certain moment, the ancestor of a certain ancient mammal has allele mutations, as long as the individual with this pair of alleles will become a male.

After a long period of evolution, the chromosome where one gene of the pair of alleles is located eventually becomes the Y chromosome, and the chromosome where the other gene is located becomes the X chromosome.

Evolving from a pair of autosomes to sex chromosomes can better adapt to sexual reproduction, and can more effectively transmit genetic material, which is the main manifestation of its beneficial mutations.

Picture: Only 45 genes left on Y chromosome

Why the Y chromosome degenerates

The degeneration of the Y chromosome did not start recently, but has been progressing slowly since autosomes became sex chromosomes in ancient times.

Human Y chromosome originally had 1438 genes, but now there are only 45. In the process of evolution, 1393 genes have been lost.

The X chromosome has a good gene "preservation rate", so why does the Y chromosome "cannot retain" genes? This may be because it is too "alternative".

Genes are subject to mutations, many of which are harmful. Chromosomes can recombine with each other gene recombination to prevent these harmful mutations from being passed on to offspring.

Picture: Schematic diagram of gene recombination

During meiosis, paternal and maternal chromosomes will be randomly mixed and paired in pairs. This random pairing can effectively eliminate harmful mutations.

This kind of beneficial pairing is possible from chromosomes 1 to 22, but Y chromosome and X chromosome cannot be recombined due to insufficient similarity.

That is to say, there may be a lot of harmful mutations accumulated on the Y chromosome, but there is no chromosome to help it resolve. Over time, these harmful mutations will be eliminated.

Biology always calculates carefully and never increases by one point. When there are fewer genes on the chromosomes, the chromosomes of genes will become smaller and smaller.

Will human males disappear

With the decrease of genes, the Y chromosome becomes smaller and smaller. If one day the gene becomes zero and the Y chromosome disappears completely, does it mean that human males will also disappear?

This sounds like a reasonable question, but will males disappear without a Y chromosome? It doesn't seem to be the case. There are ready-made examples on earth.

Some rodents such as mole voles and agouti have lost their Y chromosomes, but they still have males and females.

We usually think that sex chromosomes are very important substances. If a person has a Y chromosome, then he is a male, if not, he is a female.

But this is not the case. Studies have shown that 95% of the differences between men and women do not actually depend on sex chromosomes. For example, a gene related to female development is found on autochromosome 6.

What is the mystery that rodents can distinguish between male and female without Y chromosome? In fact, they have evolved "new sex chromosomes", which means that the functions of the original sex chromosomes are "taken over" by other chromosomes.

Human Y chromosome development direction is more likely to be similar to this, rather than after the Y chromosome disappears, there is no gene that determines male sex, so there is no male.

The magic of life lies in its completeness: no more, no more, the more will disappear slowly, and the less will slowly make up.

last

The rate of disappearance of genes on the Y chromosome is about 4.6 genes lost every 1 million years. According to this rate, the Y chromosome will lose its function in about 10 million years.

This is obviously an extremely long process. We may not have the chance to experience such mutations. But maybe someone is born with a new sex chromosome, that must be a magical thing.

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