Baby's Gender Depends on Father's Genes, Study Says

Are you planning to have a baby? The baby's gender depends on the father's undiscovered genes that control whether the sperm contains more X and Y chromosome, a study says. The research from Newcastle University involving thousands of families suggests that a potential gene controls if a man's sperm will carry more X or more Y chromosome. 

This research involved a study of almost a thousand family trees that contains information of 556,387 people from Europe and North America and dates back as far as the 1600s. It explains why some men tend to have more sons, while others tend to have more daughters.

Mr. Corry Gellatly, a research scientist at Newcastle University, explains that the study on the family trees show that whether you will have more sons or more daughters can be inherited from your parents. Men that have more brothers are more likely to have more sons, while men who have more sisters tend to have more daughters.

The sex of a baby is dependent on whether the sperm that fertilizes the mother's egg carries an X or Y chromosome. An X chromosome that combines with the mother's X chromosome will result in XX; thus, a baby girl. In the same manner, if a sperm carries a Y chromosome, the resulting XY will yield a baby boy.

A gene is composed of two parts called the alleles, and each allele is inherited from either parent. In his study, Mr. Gellatly establishes that men carry two distinct types of alleles which result in three potential combinations that affect the ratio or relation of X and Y sperm in a gene:

The first combination is the "mm," which produces more Y sperms; therefore, men with this combination tend to have more sons. The second combination is the "mf," which produces roughly equal X and Y sperms and has approximately around the same number of sons and daughters. The last combination, known as the "ff," produce more X sperms, and have more daughters.

In most of the countries that participated in the World Wars, there was a sudden upsurge in the number of sons born subsequently. After World War I, an extra two males were born for every 100 females in the United Kingdom compared to the year before the war began. Mr. Gellatly explained that the gene could explain why such occurrence transpired.

Men with more sons had more chances of having a son return from the war. On the other hand, men with more daughters had the odds against their favor. This phenomenon would explain the boy-baby boom since men who returned from the war were more likely to have boys.

In numerous countries, there are more boys than girls. In the UK and the United States, for example, the ratio is about 105 males for every 100 females are born.

Although the genetic tendency of having boys or girls is not as predictable in women, this research may help prospective parents work out whether they are likely to have sons or daughters.