Author: Jenny Graves, Distinguished Professor of Genetics and Vice Chancellor's Fellow, La Trobe University

We know that boys and girls are produced in much the same frequency. But how – and why – is this 1:1 ratio achieved? A new paper searches huge human data sets for gene variants that throw the 1:1 sex ratio off balance, and test the biological and theoretical rules of sex ratio. What produces the 1:1 sex ratio? Early scientists credited divine providence with ensuring that “every male should have its female”. Of course, we now know that sex chromosomes are the real determiners of sex. Females have two X chromosomes; males have a single X and a male-specific…