Fatherhood gene determines if it's a boy or a girl

According to recent research whether men are likely to father a boy or a girl is determined by a "fatherhood gene".

Scientists believe the fatherhood gene which is inherited from both a man's parents, comes in one of three variations and affects the number of sperm carrying male or female chromosomes.

The British scientists say because of the gene, men inherit a tendency to have more sons or daughters from their parents and a man with many brothers is more likely to have sons, while a man with many sisters is more likely to have daughters.

The scientists from Newcastle University say men with a version of the gene known as "mm" produce more sperm with the Y chromosome and are likely to have sons, while another variant, known as "mf", produces roughly equal numbers of sperm with the female X and male Y chromosomes which gives a man a 50/50 chance of having a son or daughter - the third variant, "ff", produces more X sperm and more daughters.

The study involved research into 927 family trees containing information on 556,387 people from North America and Europe dating back as far as 1600 - but despite the suggestion of the existence of three types of fatherhood gene, the gene itself remains elusive.

According to researcher Dr. Corry Gellatly, from the University of Newcastle, the system possibly balances out gender numbers and 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 the number of men and women are roughly balanced in the population.

Gellatly says if for example there are too many males in the population, females will more easily find a mate, so men who have more daughters who will pass on more of their genes, causing more females to be born in later generations.