Researchers analyzing a Utah family tree dating back to the 1700s have identified a potential selfish Y chromosome that skews sex ratios toward males. The finding, drawn from the Utah Population Database, shows 60 boys and 29 girls among 89 children over seven generations. Experts caution that the sample size is small and other factors like chance or infidelity could play a role.
A study published on bioRxiv has uncovered evidence suggesting a selfish Y chromosome may explain why some families produce mostly sons. The research focused on a large Utah family traced back over hundreds of years, using data from the Utah Population Database covering 76,000 individuals.
James Baldwin-Brown at the University of Utah described the family as "very significant." He noted that selfish genes, which bias inheritance to boost their own transmission, are known in many organisms but difficult to study in humans. In typical mammalian reproduction, sperm carry either an X or Y chromosome, leading to a 50:50 chance of male or female offspring. However, selfish variants can disrupt this balance, such as by interfering with rival sperm or killing them off.
Nitin Phadnis, also at the University of Utah, highlighted ongoing mysteries around these mechanisms, calling the question of how selfish chromosomes eliminate competitors a "100-year-old" puzzle. The team applied two statistical methods to the database, both flagging the same family as an outlier. Among 33 men who inherited the same Y chromosome across seven generations, their 89 children consisted of 60 males and 29 females—a ratio unlikely to occur by chance alone.
The data remains anonymized, preventing direct genetic sequencing of family members' sperm. Baldwin-Brown expressed interest in such analysis but acknowledged ethical and logistical challenges. SaraH Zanders at the Stowers Institute for Medical Research urged caution, pointing out that small samples can yield false signals that vanish with larger datasets. She also raised the possibility of paternity issues, though Baldwin-Brown said the team had accounted for reliable data points.
Phadnis suggested selfish Y chromosomes could contribute to high male infertility rates, as mechanisms harming half of sperm would reduce fertility. Animal studies support links between such chromosomes and infertility. The researchers plan future sperm analyses for X-Y ratios and focused on Y chromosomes due to their traceability along male lines; female-biased ratios might stem from lethal mutations rather than selfish X variants.
Broader implications include gene drives, DNA elements that spread beyond 50% inheritance rates, observed in various animals and engineered via CRISPR for applications like malaria control.
