Battle of the sex chromosomes

BMC Biology logoIt’s something of a platitude that men and women want different things, but it seems that just such a battle is fought out on the sex chromosomes. Genes that are mainly expressed in only one of the sexes – for example, those that have important roles in the ovary or testis – are distributed unequally: even though the X chromosome is found in both sexes, it contains more female-biased than male-biased genes. A common explanation for this difference is that the mammalian X chromosome is inactivated early in spermatogenesis, making it a poor location for genes necessary for sperm production.

However, according to a new study in BMC Biology, this won’t work for Drosophila. Fruit fly X chromosomes don’t seem to be inactivated during sperm production, though their genes show the same biased distribution as everyone else’s. So if it’s not meiotic X inactivation causing the difference, what is it? The authors suggest an intriguing possibility by showing that many tissue-specific genes – even those which have identical expression in each sex – tend not to be found on the X chromosome. Consequently, they hypothesize that the X chromosome is simply a bad location for genes which need to be expressed in particular tissues, and that sex differences aren’t as important as we thought.

Xuemei Lu and Chung-I Wu, discussing this mystery in an accompanying commentary, bring back the battle of the sexes. Evolutionarily, the X chromosome has spent two-thirds of its time in females rather than males, so they suggest that where genes have conflicting male and female roles – for example, if they’re used in both testes and ovaries, but have a different function in each – the female role will tend to win out. Whatever the explanation, the battle of the sex chromosomes seems set to continue.

Kester Jarvis

Senior Editor at BioMed Central
Kester is an in-house editor for BMC Biology with interests in genetics, ecology and evolutionary biology. His background is in yeast molecular biology.

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