A man’s genes play a role whether he has sons or daughters, a study of family trees has suggested.
According to the study published on sciencedaily, men also inherit a tendency to have more sons or more daughters from their parents.
This means that a man with more brothers is more likely to have sons, while a man with more sisters is more likely to have daughters.
A Newcastle University study involving thousands of families is helping prospective parents work out whether they are likely to have sons or daughters.
A research scientist at the university, Corry Gellatly, has shown that men inherit a tendency to have more sons or more daughters from their parents
The research involved a study of 927 family trees containing information on 556,387 people from North America and Europe going back to 1600.
“The family tree study showed that whether you’re likely to have a boy or a girl is inherited. We now know that men are more likely to have sons if they have more brothers but are more likely to have daughters if they have more sisters.
“However, in women, you just can’t predict it,” Mr Gellatly said.
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).
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.
On a larger scale, the number of men with more X sperm compared to the number of men with more Y sperm affects the sex ratio of children born each year.
“The gene that is passed on from both parents, which causes some men to have more sons and some to have more daughters, may explain why we see the number of men and women roughly balanced in a population.
“If there are too many males in the population, for example, females will more easily find a mate, so men who have more daughters will pass on more of their genes, causing more females to be born in later generations,” says Mr Gellatly.