Britain - Scientists discover the existence of a fatherhood gene...
[2008-12-11 The Telegraph]

http://www.telegraph.co.uk/scienceandtechnology/3703639/Scientists-discover-the-existence-of-a-fatherhood-gene.html

Thursday 11 December 2008

Science and Technology

Scientists discover the existence of a fatherhood gene

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.

By Richard Alleyne
Science Correspondent

[IMG]http://i33.tinypic.com/zvefqt.jpg[/IMG]
Men with a version of the gene produce more sperm with the Y
chromosome Photo: GETTY

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 eventaully 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."

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