Baby's gender may be determined by million-year-old virus

The sex of humans—and other mammals—may be regulated by the presence of a viral mutation that attached itself to mammalian genomes around 1.5 million years ago, according to a new study led by Yale University researchers.

The scientists found there's a mechanism that switches the virus off on the X chromosome—where an organism's sex is determined.

According to a summary of the findings, "If the level of this molecular marker is normal, X chromosomes remain active, and females and males will be born at an equal ratio. If this marker is overrepresented, X chromosomes will be silenced, and males will be born twice as often as females."

Andrew Xiao, senior author of the study, noted, "Basically, these viruses appear to allow the mammalian genome to continuously evolve, but they can also bring instability...Aside from the embryo, the only other places people have found this virus active is in tumors and neurons."

Xiao also said it's possible the viral mechanism could be used to suppress cancer.

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