GENETIC DIFFERENCES between men and women are more extensive and profound than previously believed, according to a study that unravels the chemistry of the sexes.
Analysis of the "X" chromosome - the female sex chromosome - has revealed that women are genetically more complicated than men. The findings reveal that men have taken a genetic battering that has dwindled the size of their own "Y" chromosome.
The battle of the sexes has its roots in a 300-million-year struggle between the X and the Y chromosomes which have vied with each other for influence over successive generations of males and females. Scientists showed yesterday that the X chromosome has retained its physical integrity while the Y of men has dwindled in size and power to become a shadow of its former self.
The first comprehensive survey of the genes that are active on the X chromosome has revealed the dominant position that it has gained in the long war of attrition with its male counterpart. One consequence is that boys are more prone to genetic diseases than girls.
While the Y chromosome has retained fewer than 100 working genes, the X has more than 1,000 and is able to deploy them more intricately. This has resulted in the female genome becoming very different to that of men, the scientists said. While women have two X chromosomes, men only have one, inherited from their mothers. The second sex chromosome of men is the Y of their fathers, thought to have evolved from a degenerate version of an ancient X chromosome as long as 300 million years ago.
Huntington Willard of Duke University in Durham, North Carolina, and one of the leaders of the study published in the journal Nature, said the findings show that, when the X chromosome occurs in women, it behaves so differently to when it resides in men that it has in effect resulted in the evolution of another human genome.
"We now know that 25 per cent of the X chromosome - some 200 to 300 genes - can be uniquely expressed in one sex relative to the other. In essence, therefore, there is not one human genome, but two - male and female," Professor Willard said.
Originally it was thought that one of the two X chromosomes in women was completely turned off or inactivated so that the female body did not become inundated with twice as many X-chromosome genes as men. The latest study paints a more complex and subtle picture.
Laura Carrel of Penn State College of Medicine looked at inactivity levels in the X chromosomes of 40 women. …