Preprint explores why B chromosomes experience transmission drag through the Drosophila male germline

A bioRxiv preprint investigates the transmission dynamics of supernumerary B chromosomes recently identified in a mutant Drosophila melanogaster laboratory stock. B chromosomes are accessory genomic elements found in many species that can behave as selfish genetic elements, manipulating their own inheritance at the expense of the host organism.

In the stock studied, B chromosomes exhibit drive — transmission rates above the expected 50% — when passed through the female germline, but the opposite pattern, termed drag (transmission below 50%), when inherited through the male germline. The authors set out to determine whether male fertility defects could explain the reduced transmission through males, concluding that fertility is not impaired. This rules out one candidate mechanism and directs attention towards other potential explanations, such as meiotic or post-meiotic processes specific to the male germline.

The study contributes to understanding of selfish genetic elements and the evolutionary arms races between such elements and host-derived suppression mechanisms. The findings are specific to a laboratory stock and their generalisability to natural populations or other species would require further investigation. The work has not yet been peer reviewed.