In cell biology, men and women are unequal: men have an X chromosome, while women have two. How can we get around this difference? Geneticists from the University of Geneva (UNIGE), Switzerland, turned to some historic research dating from the 1960s to sequence skin and blood cells one by one. They observed how the second X chromosome in females gradually becomes inactive in order to avoid an overdose of genes encoded by the X. They also found that several genes bypassed this inactivation, which varied according to the tissue and life phases of the cell. The UNIGE research explains the inequalities noted between men and women regarding genetic diseases. You can read all about the results in the journal PNAS.