Y?

This post will be of keen interest to only around half of us. What is the history of the Y-chromosome?

It seems that they started off minding their own business being standard chromosomes but over the course of time 2 unique characteristics have developed.

Firstly, the Y chromosome has hardly any interaction with its partner, the X chromosome. (Normally recombination can happen between chromosome pairs).

Secondly, the number of active genes on the Y chromosome is greatly reduced – it is almost devoid of functional genes. Of the few genes that are there, most (unsurprisingly) are related to male development and fertility.

This process has happened repeatedly in different parts of the animal kingdom, and by looking at Y chromosomes at different stages in living species scientists are able to suggest a general mechanism.

The most primitive state is either hermaphroditism, or where the gender is determined by environmental factors – in other words there is no genetic influence and there is nothing particularly significant in the appearance of the chromosomes. Then there is a stage where small groups of genes start to influence gender, followed by semi-chromosomal selection, and finally a full blown chromosomal situation where XX = female, XY = male.

Studies suggest that the human Y-chromosome started keeping himself to himself around 300 million years ago. Now there are only 19 genes left on Y that have a corresponding partner on X.

The few areas where the sequence on a Y chromosome matches the sequence on an X can be thought of as ‘fossils’ that reveal the evolutionary history that goes before.