We know that women live longer and are less susceptible to certain diseases than men. That may be down to the benefits of having two X chromosomes
29 July 2020
WOMEN generally outlive men and are less susceptible to certain illnesses – including covid-19, it now appears. Why health outcomes are so drastically different between the sexes is unclear. But Sharon Moalem, a doctor and genetic researcher based in New York, thinks he has the answer. It isn’t because women tend to go to the doctor more or have healthier habits, he says. Instead, it’s because they are typically better equipped, genetically speaking.
In humans, sex is largely determined by chromosomes, the bundles of tightly coiled DNA that carry our genes. The cells of most women possess two X chromosomes while most men have one X and one Y. So that women’s cells don’t have to carry two versions of each gene on the X chromosome, one from each X, one of the Xs is mainly switched off. It appears that which one stays active in which cells is chosen seemingly at random some time during the first few weeks of pregnancy. The result is that half a women’s cells generally use the X chromosome she inherited from her mother, while the other half use the one from her father.
It has long been known that if one X has a harmful mutation, cells that use the other X can compensate. That’s why, for instance, women are less likely to be colour-blind; a gene important for eye function resides on the X chromosome. Yet Moalem argues that the benefits are far more significant than this alone. He makes the case that even if there is no obviously harmful mutation, women tend to be at an advantage by having bodies …