The claim: Some men are more likely to father boys
The facts: Men who want to know whether they are more likely to father a boy or a girl may now be able to find an easy clue: consult your family tree.
It has long been suspected that men who come from families with plenty of males have higher odds of fathering boys and that for men with many sisters, it is vice versa. However, there was never any strong evidence. So last December, a British doctoral student put the theory to the test.
In a study published in the journal Evolutionary Biology, researcher Corry Gellatly examined the histories of more than 900 Americans and European families dating to 1600, involving more than half a million people.
A child’s sex is always determined by the father, since men cast the deciding chromosome – either an X or a Y – while women produce eggs that carry an X chromosome. Mr Gellatly found evidence that men carry a gene that determines the percentage of X and Y chromosomes in their sperm and that the gene comes in three alleles, or versions. One produces mostly X chromosomes, another mostly Y, and the third yields equal numbers of both.
However, carrying a gene that predisposes men to more sons or daughters is no guarantee, in the same way that rolling a rigged die with a six on four of its faces is no guarantee of landing a six.
The bottom line: Some men, it seems are genetically morel likely to sire more boys than girls, and vice versa
- The New York Times