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Existence of fatherhood gene discovered
(Agencies)
Updated: 2008-12-11 10:14 Men with lots of brothers are more likely to have sons than daughters, scientists claim after studying family trees dating back more than 400 years.
Researchers believe the study points to the existence of a fatherhood gene which determines whether men are likely to father boys or girls. Even though they have not been able to identify the gene it is believed that eventually it could lead to a test to determine the likely sex of offspring. The inherited gene comes in one of three variations and affects the number of sperm carrying male or female chromosomes, they claim. Men with a version of the gene known as "mm" produce more sperm with the Y chromosome and are likely to have sons. Another variant, known as "mf", produces roughly equally numbers of sperm with the female X and male Y chromosomes. In this case, a man has a 50/50 chance of having a son or daughter. The third version, "ff", produces more X sperm and more daughters. Because of the gene, men inherit a tendency to have more sons or daughters from their parents, say scientists. A man with many brothers is more likely to have sons, while a man with many sisters is more likely to have daughters. The research, published online in the journal Evolutionary Biology, involved a study of 927 family trees containing information on 556,387 people from North America and Europe going back as far as 1600. Although it suggests the existence of three types of fatherhood gene, the gene itself remains undiscovered. Researcher Corry Gellatly, from the University of Newcastle, said the system would tend to balance out gender numbers. "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," he said. It could also explain sudden increases in the numbers of boys born after the two world wars. The year after the First World War ended, an extra two boys were born for every 100 girls in the UK compared with the year before war broke out. Mr Gellatly explained that the odds were in favour of men with more sons seeing a son return from the war. These were likely to be men with the "mm" gene variant. Survivor sons who inherited this version of the gene, would in turn be more likely to have sons themselves. In contrast, men with more daughters may have lost their only sons in the war. Those sons would also have been more likely to father girls. "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," said Mr Gellatly. "However, in women, you just can't predict it." |
