Rare genetic mutation linked to higher likelihood of daughters

Globally, the number of boys and girls born is nearly equal; however, some families exhibit a clear predominance of one gender among their children. Scientists sought to explore this phenomenon by investigating its genetic determinants.

Jianzhi Zhang, an evolutionary geneticist at the University of Michigan, has examined this issue for years. He noted that previous studies have not conclusively confirmed the existence of genetic variability that affects the sex ratio among humans.

"Scientists have been pondering and researching a genetic basis for sex ratio for decades, yet no unambiguous evidence for a genetic variation that alters the human sex ratio from an approximately 50:50 ratio has been found," explained Zhang.

He also pointed out that almost all human traits result from genetic variability, making the lack of impact of mutations on the sex ratio seem unlikely.

One of the main challenges of previous studies was the difficulty of accurately measuring the sex ratio of a person's children, making it hard to detect genetic influence. To address this issue, Zhang and his doctoral student, Siliang Song, analyzed data from the UK Biobank, a massive database covering approximately 500,000 participants from the United Kingdom.

Through this study, they identified a rare mutation, rs144724107, that increases the chances of having a daughter by 10 percent. However, this mutation is present in only about 0.5 percent of those studied.

This mutation is located near the ADAMTS14 gene, which is involved in the processes of spermatogenesis and fertilization, potentially explaining its impact on the sex ratio. However, scientists emphasize that this discovery requires further research to confirm its validity in other population samples.

Further analysis also identified two other genes, RLF and KIF20B, which may play a similar role in regulating the sex ratio. These findings are consistent with Fisher's principle, an evolutionary theory that states natural selection promotes genetic variants that increase the number of rarer sexes in the population, ultimately leading to balance.

Professor Zhang also highlighted the potential applications of these studies in agriculture. In many areas of livestock breeding, such as egg or milk production, one sex—usually females—is preferred. Genetic modifications aimed at increasing the number of animals of this sex could provide significant economic benefits while reducing the number of animals of lesser economic value, such as young males, often culled shortly after birth.

Although the study's results are promising, scientists know the challenges they may face in verifying them. The rarity of the mutation and the need to analyze large groups of subjects present challenges for further research.