INHERITANCE OF LITTER SIZE AT BIRTH IN THE HOUSE MUSK SHREW (SUNCUS-MURINUS, INSECTIVORA, SORICIDAE)

In this research we estimated the contribution of a major-gene effect to the control of litter size in hybrids between two local populations of the house musk shrew (Suncus murinus). Segregation analysis was pe rformed on the basis of a mixed polygene and major-gene model. The mod el presumes that two parental populations may differ from each other i n gene frequencies and in the values of polygenic effects but not in t he major-gene contribution of the trait. Moreover, the peculiarity of the trait - litter size - is taken into account. This trait is not an individual attribute. It characterizes the parental couple and may dep end on the genotypes of both parents. Results of segregation analysis of a large hybrid pedigree of Suncus murinus indicate that the parenta l populations differ in the allele frequency of the major gene (one po pulation is homozygous, while the other contains the two alleles in ap proximately equal proportions) and in the values of average polygenic effects. Both major-gene and polygenic components are necessary for th e correct description of litter size inheritance in interracial hybrid s of S. murinus, inasmuch as the exclusion of either of them leads to a significant drop in likelihood. The Elston-Stewart criterion also co nfirms the Mendelian inheritance of the major gene.