Millions Fewer Girls Born Due to Nuclear Radiation?

Female Chromosomes Especially Vulnerable?

The biological mechanism behind the skewed sex ratio wasn't investigated in the study. But previous radiation experiments on animals suggest the boost in males may be due to damage to X chromosomes in sperm, Scherb said.

In humans, a sperm cell contains either an X or Y chromosome, while an egg contains no Y chromosome. If an embryo has an XY combination, it will become a boy. An XX combination results in a girl. (Get a genetics overview.)

It's not known exactly why X chromosomes in sperm would be more likely to sustain radiation damage than Y chromosomes or in X chromosomes in eggs, Scherb said. Perhaps it's because X chromosomes are simply bigger targets or because eggs insulate their chromosomes better than sperm cells do, he speculated.

It could also be that, because X chromosomes--being larger than Y chromosomes--carry more genes, X chromosome damage is more likely to result in a fatally deformed embryo, he said.

Information on the study's co-author and institution:    Institute of Biomathematics and Biometry

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