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Men and women differ in obvious ways for example, in the prevalence of certain diseases or reactions to drugs.
Weizmann Institute of Science researchers recently uncovered thousands of human genes that are expressed out to make proteins differently in the two sexes.
Pietrokovski and Gershoni showed that mutations in genes specific to sperm formation persist precisely because the genes are expressed only in men.
A mutation that is problematic for only half of the population, no matter how detrimental, is freely passed on to the next generation by the other half.
In this study, the researchers expanded their analyses to include genes that, though not necessary for fertility, are still expressed differently in the two sexes.
To identify these genes, the scientists used a very large study of human gene expression recorded for numerous organs and tissues in the bodies of close to 550 adult donors.
Pietrokovski and Gershoni looked closely at around 20,000 protein-coding genes, sorting them by sex and searching for differences in expression in each tissue. They eventually identified around 6,500 genes with activity that was biased toward one sex or the other in at least one tissue.
For example, they found genes that were highly expressed in the skin of men relative to that in women’s skin, and they realized that these were related to the growth of body hair. Gene expression for muscle building was higher in men; storage were higher in women.
Apart from the sexual organs, the researchers discovered quite a few sex-linked genes in the mammary glands — not so surprising, except that about half of these genes were expressed in men.
The researchers also identified gene expression in the liver in women that regulates drug metabolism, providing molecular evidence for the known difference in drug processing between women and men.