Abstract
Selfish genetic elements that bias their inheritance to the detriment to their host are in an evolutionary arms race with host-derived suppressors that neutralize the spread of these elements. The supernumerary B chromosomes recently found in a mutant
Drosophila melanogaster
laboratory stock are subject to drive (>50% transmission) when passed through the female germline, but through the male germline they experience the opposite of drive, a phenomenon referred to as drag (D. melanogaster
, which is poised to significantly advance on our understanding of how various genetic and developmental contexts promote disparate chromosome behavior.