Meiosis and fertility in common shrews, Sorex araneus, from a chromosomal hybrid zone in central Sweden.

Adult male common shrews from the Uppsala and Hällefors Robertsonian chromosomal races and hybrids were collected from the area of Surahammar in Sweden. Meiosis and fertility of hybrid (complex heterozygotes) and nonhybrid (homozygotes) individuals were compared based on an analysis of chromosomal interactions and synapsis at pachytene, chiasma characteristics at diakinesis, and germ-cell death. No individuals suffered severe germ-cell loss, and the differences found among the Uppsala and Hällefors homozygotes and the hybrids were not significant. In complex heterozygotes, ring configurations of four elements were observed at meiosis I, with one chiasma per chromosome arm. Abnormal rings were frequent at pachytene, but interactions between the ring and other chromosomes were seldom found. There is no indication from this study of a differential fertility between homozygotes and ring IV-forming complex heterozygotes in males.