Boy or girl? It’s in the father’s genes

Posted on July 1, 2019

The sex of a baby is usually dependent on whether their sperm is carrying an X or Y chromosome. An X chromosome combines with the mother’s X chromosome to make a baby girl (XX) and a Y chromosome will combine with the mothers to make a boy (XY).

A Newcastle University study involving thousands of families is helping prospective parents work out if they are likely to have sons or daughters.

A Newcastle University study suggests that a possible gene controls if a man’s sperm becomes more X or more Y chromosomes, which affects the sex of his children. A gene consists of two parts, known as alleles, one inherited from each parent. Mr Gellatly demonstrates that it is likely men carry two different types of allele, which results in three possible combinations in a gene that controls the ratio of X and Y sperm.

It is found that men with ‘mm’ combination, produces more Y sperm and have more sons. The second combination, 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’ produces more sperm and have more daughters.

In many countries that fought in the World Wars, there was a sudden increase in the number of boys born afterwards. The year after WWI ended, an extra two boys were born for every 100 girls in the UK, compared to the year before the war started. The gene, which Mr Gellatly has described in his research, could explain why this happened.

As the odds were in favour of men with more sons seeing a son returning from the war, those sons were more likely to father boys themselves because they inherited that tendency from their fathers. In contrast, men with more daughters may have lost their only sons in the way and those sons would have been more likely to father girls. This would explain why the men that survived the war were more likely to have male children, which resulted in the boy-baby boom.

Category(s):Pregnancy & Birthing

Source material from Science Daily

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