CHROMOSOMAL SEGREGATION AND FERTILITY IN ROBERTSONIAN CHROMOSOMAL HETEROZYGOTES OF THE HOUSE MUSK SHREW (SUNCUS-MURINUS, INSECTIVORA, SORICIDAE)

Crucial to our understanding of chromosomal variation and evolution in mammals are detailed studies of chromosomal heterozygotes, with analy ses of chromosomal segregation and chromosome-derived infertility. We studied segregation and fertility in hybrids between karyotypic races of the house musk shrew Suncus murinus. These individuals were heteroz ygous for up to five Robertsonian fusions (Rbs) and an insertion of he terochromatin in an autosome. All variant chromosomes showed Mendelian segregation and all Rbs segregated independently of each other in the progeny of double heterozygotes. Litter size in single and even multi ple Rb heterozygotes was no smaller than that in the less fertile pare ntal strain. The effects of genetic background were more important in determining litter size than Rb heterozygosity for the shrews that we examined.