Size difference between a X chromosome (big) and a Y chromosome (small)

It was thought that Y chomosome was a degeneration of X crhomosome and whose only function was to create the testicles and to produce the sperm and it will eventually dissapear. Some scientific researches have denied these beliefs and show the truth about the Y crhomosome.

Y chromosome appeared during the period of separation between marsupials and mammals. It started to lose genes  but it stabilized 25 million years ago, as two researches of Lausana University and MIT  (Massachusetts Institute of Technology) have shown.

Y chromosome has not been studied in genome proyects: due to its repetitive and palindromic sequences DNA readers couldn’t analyze them. Researchers have solved those technical problems and they have secuenced the Y chromosome of the rat, the mouse, a small monkey, and the opossum. Those have been compared between them and with those which had already been studied (macaque, chimpanzee, and human).

This shows that only the 3% of the genes the initial Y chromosome appears in at least one of the actual mammals. Y chromosome lost a great part of genes, but after it stongly stabilized, that seems to be a selective process, where only necessary material is kept.

36 genes of Y chromosome are in X chromosome too, and they are the same in all the studied mammals. This has almost not change between humans and apes during the last 25 million years. Most of these genes are controller genes, probably because of that, Y chomosome has been kept.

Y chromosome function is not just to make the fetus a male, but it will affect the genome during the whole life. This chromosome has a specific function so it will not disappear


This study has been carry out by the Massachusetts Istitute of Technology, Boston, and by the Lusana University.

The new has been selected from the digital version of the newspaper ‘El País’, this is the link to the new:

La evolución de la virilidad- El País

I took some information from the research of David Page, a teacher in the MIT:

Theory of the ‘rotting’ chromosome dealt a fatal blow-Whitehead Institute (by Matt Fearer)

An article has been published in Nature too

“Strict evolutionary conservation followed rapid gene loss on human and rhesus Y chromosomes”- Nature 



I found this research so interesting, because it helps us to have more knowledge about human beings. It shows that differences between women and men go further than we thought, there are differences about the way genes are controlled too. This could make a difference about the way we have to study those illness which are more common in one gender than in other, and that way, solve them easilier.

In the other hand, it is a great advantage to be able to sequence the Y chromosome, which has been a mystery during a long time. Some people thought it was a defective X chromosome but now it is clear that it has appeared through natural selection to carry out a necessary job and is not a failure.

Esta entrada foi publicada en Bioloxía - Fisioloxía, Biotecnoloxía, Xenética, Curso 2013-2014, Evolución, paleontoloxía, Saúde. Ligazón permanente.


  1. You may have noticed this sentence from El Pais
    “El cromosoma Y ha sido el gran olvidado de los proyectos genoma, por razones técnicas: está plagado de secuencias repetitivas y palindrómicas –que se leen igual al derecho y al revés— que constituyen la pesadilla de cualquier máquina de leer ADN”.

    Palindromes are mentioned in your original source, as you can check in the Abstract. Besides that, it is possible to find the complete article (by typing the whole title in google), and so you’d read:
    ‘(…) in human and chimpanzee, the MSY’s ampliconic regions feature large palindromes, each composed of two inverted repeats (arms) separated by a short spacer. The human and chimpanzee MSYs have, respectively, eight and 19 palindromes (…) By contrast, the rhesus MSY has only three palindromes’

    So, can you explain the role palindromes may play in Y chromosome? Maybe you’ll find this reference useful.

    All of us have spelling mistakes when typing, it doesn’t matter here. But remember a couple of things: (1) ‘Actual’ is a false friend, and (2) ‘link to the new’ is a literal translation from Spanish, it should be ‘link to the piece of news’

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