Non-disjunction frequency in male complex Robertsonian heterozygotes of the common shrew

Common shrews display two types of Robertsonian (Rb) heterozygosity: simple (where CIII configurations are formed at meiosis 1) and complex (which have longer meiotic chains or rings). Based on an analysis of large sample sizes (over 100) of MII cells per specimen, we estimated the non-disjunction frequency in seven Rb homozygotes and 21 complex Rb heterozygotes (CIV and CV) of Sorex araneus Linnaeus, 1758. The analysis showed high between-individual variability. The mean level of non-disjunction in homozygotes (2.01%) was significantly lower than in CIV and CV heterozygotes (4.27% and 5.78%, respectively). The study demonstrated that non-disjunction frequelicy in male CIV and CV heterozygotes was similar to that in simple heterozygotes in the common shrew.