An Autosomal Factor From Drosophila arizonae Restores Normal Spermatogenesis in Drosophila mojavensis Males Carrying the D. arizonae Y Chromosome <B>An Autosomal Factor From Drosophila arizonae Restores Normal Spermatogenesis in Drosophila mojavensis Males Carrying the D. arizonae Y Chromosome</B><P> </B><B>A. C. Pantazidis(1,2), V. K. Galanopoulos(1,2) and E. Zouros(1,2,3)</B><I><P> (1) Institute of Molecular Biology and Biotechnology (FO.R. T.H.), Heraklion 711 10, Crete, Greece,<BR> (2)Department of Biology, University of Crete, Heraklion 711 10, Crete, Greece<BR> (3)Department of Biology, Dalhousie University, Halifax, Nova Scotia, B3H 4JI, Canada</I><P> Manuscript received August 13, 1992<BR> Accepted for publication January 26, 1993<B><P> Abstract</B><P> Males of <I>Drosophila mojavensis </I>whose<I> Y</I> chromosome is replaced by the <I>Y</I> chromosome of the sibling species <I>Drosophila arizonae</I> are sterile. It is shown that genetic material from the fourth chromosome of <I>D. arizonae</I> is necessary and sufficient, in single dose, to restore fertility in these males. In introgression and mapping experiments this material segregates as a single Mendelian factor (sperm motility factor, <I>SMF</I>). Light and electron microscopy studies of spermatogenesis in <I>D. mojavensis </I>males whose <I>Y</I> chromosome is replaced by introgression with the <I>Y</I> chromosome of <I>D. arizonae</I> (these males are symbolized as <I>mojYa</I>) revealed postmeiotic abnormalities all of which are restored when the <I>SMF</I> of <I>D. arizonae</I> is co-introgressed (these males are symbolized as <I>mojYaSMFa</I>)<I>. </I>The number of mature sperm per bundle in <I>mojYaSMFa </I>is slightly less than in pure <I>D. mojavensis </I>and is even smaller in males whose fertility is rescued by introgression of the entire fourth chromosome of <I>D. arizonae. </I>These observations establish an interspecific incompatibility between the <I>Y</I> chromosome and an autosomal factor (or more than one tightly linked factors) that can be useful for the study of the evolution of male hybrid sterility in Drosophila and the genetic control of spermatogenesis.<I><P> Genetics</I> 134: 309-318 (May 1993)<P>