A Father’s Genes May Determine Their Child’s Sex

Kristin Osika

By: Kristin Osika ’22

Many soon to be parents have one question in mind: “Will our child be a boy or a girl?” Sex has always been thought to be a matter of fate. Many believe it is just as likely for two parents to have a son or a daughter because of the role chromosomal inheritance plays in determining sex. A child’s sex is determined by the sex chromosome they inherit from their father. With the inheritance of an X chromosome, the child will be female, and with the inheritance of a Y chromosome, the child will be male. The child supposedly has an equal chance of inheriting either the X or Y chromosome.

What if sex determination is more complex than scientists originally anticipated? A researcher at Newcastle University used 927 family trees dating back hundreds of years to study sex inheritance patterns. The study analyzed over 500,000 people of American and European descent to determine if the likelihood of having a boy or girl can be inherited. The researcher identified patterns which indicated that men with brothers are more likely to have sons, and men with sisters are more likely to have daughters. 

The research suggests the pattern appearing in males is the result of an unidentified gene. This gene might cause men to have more X or Y chromosomes, resulting in a higher likelihood they would have daughters or sons, respectively. 

The discovery of this gene might explain certain sex patterns throughout history. For example, after World War II, countries such as England noticed an increased amount of males born compared to females. In the war, many families with fewer sons lost all their sons. Families with more sons, on the other hand, were more likely to have at least one son who survived the war. Men who had more brothers were more likely to produce male offspring as a result of the gene, and therefore, more male children were born overall in England after the war.

While this gene could prove as a breakthrough in identifying sex determination patterns in males, researchers found no traceable pattern in females. They suspected women might carry this gene without expressing it, meaning they lack any impact on sex determination. 

Additional research is being conducted to determine the role of this newly discovered gene in sex inheritance, and to trace this identified pattern further. In the future, predicting a child’s sex might be as easy as looking at the father’s family tree.


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