Arlt, who is also the first author of the study, further noted that if certain genes gave X-bearing sperm an advantage, the result would be more female offspring—the same goes for Y-bearing sperm and male offspring. Yet, he noted that the sex ratio remains close to 50-50. Over evolutionary time, this balance is optimal for the survival of a species, while even small shifts could eventually threaten its stability.
To maintain the sex-ratio balance, genes on the X and Y chromosomes co-adapt, regulating each other’s influence. However, how this process works remains a mystery as sperm cannot be grown in a lab. The University of Michigan team found a creative solution by transferring the X-linked Slxl1/Slx and Y-linked Sly gene families from mice into yeast, enabling them to study the genetic interactions in a controlled environment.