A new study is currently looking at families and helping them determine whether they are more likely to have a boy or a girl.
Scientists from Newcastle University found that men inherit from their parents a tendency to have more sons or more daughters. In simpler terms, a man with more brothers is likely to have sons, and a man with more sisters is likely to have a daughter.
The study involved 927 family trees with information on 556,387 people from North America and Europe. These family trees dated back to the year 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,” said Corry Gellatly, a research scientist at the university.
The study suggests that there may be an undiscovered gene that controls whether the sperm contains more X or Y chromosomes, thereby affecting the sex of the child.
The researchers say that men may carry two different types of allele, resulting in three possible combinations in a gene controlling X and Y sperm ratio.
- Men with the first combination, known as mm, produce more Y sperm and have more sons.
- The second, known as mf, produce a roughly equal number of X and Y sperm and have an approximately equal number of sons and daughters.
- The third, known as ff produce more X sperm and have more daughters.
This diagram illustrates how the gene works
"In the first family tree (A) the grandfather is mm, so all his children are male. He only passes on the m allele, so his children are more likely to have the mm combination of alleles themselves. As a result, those sons may also have only sons (as shown). The grandsons have the mf combination of alleles, because they inherited an m from their father and an f from their mother. As a result, they have an equal number of sons and daughters (the great grandchildren)."
"In the second tree (B) the grandfather is ff, so all his children are female, they have the ff combination of alleles because their father and mother were both ff. One of the female children has her own children with a male who has the mm
combination of alleles. That male determines the sex of the children,
so the grandchildren are all male. The grandsons have the mf combination of alleles, because they inherited an m from their father and f from their mother. As a result, they have an equal number of sons and daughters (the great-grandchildren)."
“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,”
This study also looked at the boy-baby boom which occured after the World Wars and explained that men who survived the war were more likely to have male children.
This research was published on December 11 in the journal Evolutionary Biology.
Source: Newcastle University Press Release