The X Advantage

Genetic research into differences between the sexes is increasingly showing that the extra X chromosome in women helps them fight off disease and may be the reason for their increased lifespan. Men are born with one X chromosome and a much smaller and relatively "weak" Y chromosome, which is involved in the development of male characteristics. Women are born with two X chromosomes.

In the United States, according to 2003 U.S. Census data, women live an average of 80.1 years, while men only live an average of 74.8 years. More males die of chromosomal defects than females do.

The X chromosome has about 1,100 genes on it that are involved in blood clotting, muscle function, and ridding cells of waste, among other things. It may also be the reason why girls comprehend colors differently, develop different personality traits and acquire longer attention spans. If a defect or mutation occurs on the X chromosome in a male, he is stuck with the defect whereas females have a back-up copy of the chromosome. Females can be considered "mosaics," since in a given cell only one of the X chromosomes can be expressed. Cells can express either the father's X chromosome genes or the mother's X chromosome genes in a cell, which leads to more variety overall.

Though the article does not mention it, it probably is incorrect to assume that the X chromosome is the only reason females, on average, live longer than men. There are many factors contributing to longevity, including nutrition, environment, occupation, and lifestyle, to name a few. But the article provides compelling evidence to suggest that the double X chromosome is at least part of the reason.

HealthDay News Article
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