Boys or girls depend on their father

A Newcastle University study with the participation of thousands of families is a solution for parents about whether they have a son or a daughter.

Research by scientist Corry Gellatly shows that men inherited from parents tend to have more sons or more daughters. This means that a man with many brothers is more likely to have a son, while a man with many sisters is more likely to have daughters.

The study was based on the information of 927 family genealogies and 556,387 people from North America and Europe from the 1600s.

Gellatly explains: 'Family genealogies show a tendency to have a son or a daughter with genetic characteristics. Now we know that men are more likely to have a son if they have many brothers, and are more likely to have daughters if there are many sisters. However, for women, you cannot predict anything. '

Men determine the sex of a child based on their sperm containing the X or Y chromosome. An X chromosome combined with another X chromosome from the mother will form a girl (XX). , and a Y chromosome combined with the mother's chromosome will produce a boy (XY).

The Newcastle University study showed that an undiscovered gene controls whether male sperm contains more X chromosomes or more Y chromosomes. This affects the sex of the child being born.On a larger scale, the number of men with sperm contains more X chromosomes than the number of men with more Y chromosomes affecting the sex ratio of children born each year.

Son or daughter?

A gene contains two parts, called the corresponding gene, inherited from parents. In his paper, Gellatly demonstrates that it is very likely that men contain two different types of corresponding genes. This leads to three possible combinations of a rate control gene for X and Y sperm.
• The first type of combination, called mm, produces more Y sperm and has more sons.
• The second type of combination, called mf, produces the same amount of X and Y sperm, and has the same number of sons and daughters.
• The third type of combination, called ff, produces more X sperm and more daughters.

Gellatly said: 'Genes inherited from both parents cause some men to have more sons and others have more daughters, which may explain why the number of men and women is equivalent. If there are too many men in the community, women will easily find partners, so men with more daughters will inherit more of their genes, making more girls born in those situations. Next generation '.

Many boys were born after the war

In many countries participating in the war in the world war, the number of boys born often increased suddenly after the war. The year after the First World War ended, two more boys were born to over 100 girls in the UK when compared to the year before the war began. Genes described by Gellatly in their study may explain why this phenomenon occurred.
Men with more sons, probably one of them returned from the front and also tended, inherited from his father, to become the father of boys. On the contrary, men with more daughters may lose the only child in the war. These people tend to be the father of girls. This explains why the men who survived the battle tend to have boys and make the rate of boys born increased sharply.

A simplified chart shows that men have only sons or only daughters, or the same number of sons and daughters. (Photo: Newcastle University)

In most countries, in the data exist, there are always more boys than girls born. In the United Kingdom and the United States, there are 105 boys born over 100 girls.

There is also a lot of documentation that many boys die prematurely before being mature enough to have children. So similar to the gene that causes many boys to be born after the war, it can also cause many boys to be born each year.

Genetic activity?

Genealogy (above) illustrates gene activity. This is a simplified example, in which men only have sons, or only girls, or the number of sons and daughters is equal. It shows that although this gene does not affect women, they also carry that gene and inherit it to their children.

In the first family tree (A), the grandfather is mm, so all children are sons. He showed the corresponding gene to be m, so his children were more likely to form a mm combination. Therefore, sons may only give birth to boys. The grandchildren may have mf combinations of genes, because they inherit m from f and f from their mothers.Therefore, they have the same number of sons and daughters (great grandchildren).

In the second genealogical tree (B) the grandfather is ff, so there are only daughters, and they have the corresponding ff gene combination, since both their parents both carry the ff gene. One of the daughters had a child with a man with a mm combination. The man decides the sex of the children, so his grandchildren are all boys. The grandchildren have the mf combination of genes, because they inherited m from f and f from their mothers. Therefore, they have equal numbers of sons and daughters.

Refer:
1. Gellatly et al.Trends in Population Sex Ratios May Be Explained by Changes in the Frequencies of Polymorphic Alleles of a Sex Ratio Gene.Evolutionary Biology, Dec 11, 2008;DOI: 10.1007 / s11692-008-9046-3