Is a 'selfish gene' making a Utah family have twice as many boys as girls?

"Such sex 'distorters' have been discovered - and studied in great depth - in laboratory animals such as mice and flies, in which their effects can be detected through selective breeding. 'If you look, more often than not, you find them,' says Nitin Phadnis, an evolutionary geneticist at the University of Utah in Salt Lake City, who co-led the study."

"Theoretical predictions suggest that sex distorters probably do exist in people as well, and that they could produce excesses of biological boys or girls at birth. But humans' long generation times and low birth rates as well as ethical issues have made such genes - and other 'selfish' genetic elements difficult to spot."

"In humans, biological sex is determined by the sex chromosome that fathers pass onto their offspring: each sperm cell typically carries either a Y or an X chromosome, but not both. The mother's egg cell, by contrast, usually carries a single X."

Researchers discovered a Utah family exhibiting a seven-generation pattern of producing twice as many boys as girls, suggesting the existence of 'selfish genes' that distort offspring sex ratios in humans. Such sex-distorting genes have been well-documented in laboratory animals like mice and flies but have been difficult to identify in humans due to long generation times, low birth rates, and ethical constraints. The study utilized the Utah Population Database, containing genealogical and health data spanning from the late eighteenth century to present day. Biological sex determination depends on the sex chromosome fathers transmit: Y chromosomes produce male offspring while X chromosomes produce female offspring. This discovery represents the first clear evidence that humans may possess genetic elements capable of biasing their own transmission regardless of fitness benefits.

Read at Nature