Location of an autosomal factor causing sterility in Drosophila mojavensis males carrying the Drosophila arizonensis Y chromosome.

Drosophila mojavensis males whose Y chromosome is replaced by the Y of D. arizonensis, have immotile sperm. Sperm motility is restored if one member of the fourth autosome pair is also replaced by an arizonensis homologue. We present evidence that the effect of the fourth chromosome is due to a single Mendelian factor and map this factor relative to the two markers available for this chromosome. This is an essential first step towards understanding the nature of the incompatibility between the arizonensis Y chromosome and the mojavensis fourth chromosome responsible for this type of post-zygotic isolation between these closely related species.