Just read this interesting article at bbc online . here is an extract from the article below.
A man’s genetic make-up may play a role in whether he has sons or daughters, a study of hundreds of years of family trees suggests.
Newcastle University researchers found men were more likely to have sons if they had more brothers and vice versa if they had more sisters.
They looked at 927 family trees, with details on 556,387 people from North America and Europe, going back to 1600.
The same link between sibling sex and offspring sex was not found for women.
The precise way that genes can influence baby sex remains unproven.