Scientists have long wondered why women outlive men globally. Now, they have found that the secret may lie in the second X chromosome, present in females. The study, conducted on mice, showed that females live longer than males and that XX largely governs this trait in ageing mice. The researchers from the University of California San Francisco (UCSF) gave experimental mice four different combinations of chromosomes and gonads: the two found in nature -- XX with ovaries and XY with testes -- and two others created in the laboratory -- XX testes and XY ovaries. The X chromosome contains many
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