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As a result, they have an equal number of sons and daughters (the great-grandchildren).

Citation: Evolutionary Biology, DOI 10.1007/s11692-008-9046-3 Source: Newcastle University This document is subject to copyright.

Men determine the sex of a baby depending on whether their sperm is carrying an X or Y chromosome.

An X chromosome combines with the mother's X chromosome to make a baby girl (XX) and a Y chromosome will combine with the mother's to make a boy (XY).

He only passes on the m allele, so his children are more likely to have the mm combination of alleles themselves.

As a result, those sons may also have only sons (as shown).

The Newcastle University study suggests that an as-yet undiscovered gene controls whether a man's sperm contains more X or more Y chromosomes, which affects the sex of his children.

Last modified 12-Dec-2019 13:23