At least 6,500 genes are expressed at different levels in male or female body tissues, finds a new study.
'The basic genome is nearly the same in all of us, but it is utilized differently across the body and among individuals,' said Dr Moran Gershoni, who carried out the study, published in BMC Biology, with Professor Shmuel Pietrokovski at the Weizmann Institute of Science, Israel.
Using data from the GTEx project – a large study of human gene expression in different organs and body tissues from nearly 550 adult donors – the researchers investigated the expression levels of 20,000 different genes, and sorted their findings by sex and tissue.
Of the genes they studied, close to 6500 had an expression level that was biased towards one sex or the other in at least one tissue type. For example, genes related to hair growth were expressed more highly in men's skin cells than women's, while genes related to fat storage were expressed more highly in women.
Interestingly, they found that genes with a higher sex-specific expression bias accumulated mutations at a much higher rate than genes with a similar expression level between the sexes.
'The more a gene was specific to one sex, the less selection we saw on the gene,' said Dr Gershoni.
Differential gene expression between the sexes could explain why certain mutations can persist in the population, and the authors speculate that this could help researchers understand why rates of infertility between couples are so high. For example, women can pass on mutations that might be highly detrimental to male fertility, as they do not hinder female reproduction.
'Paradoxically, sex-linked genes are those in which harmful mutations are more likely to be passed down, including those that impair fertility,' said Professor Pietrokovski.
Their findings also identified potential differences in disease onset and response to drug treatment between the sexes. It is hoped that these findings could aid disease research and treatment in the future.
Notably, the expression of one gene, called NPPB, was found to decline in women with age, which the researchers suggest might play a role in the increased risk of heart disease found in post-menopausal women.
They also found that genes for certain enzymes in the liver, which are known to regulate drug metabolism, were expressed more highly in women than men. This provides a degree of evidence for the differences observed in drug processing between men and women, they suggest.
'The study also emphasizes the need for a better understanding of the differences between men and women in the genes that cause disease or respond to treatments,' said Professor Pietrokovski.