Variation and Inheritance of an Atypical form of the Anterior Lobe of the M1 of Lemmus trimucronatus chrysogaster (Rodentia, Arvicolinae)

Using material from laboratory colonies, it was established that the variability of deviations from the typical shape (tf) of the anterior lobe M1 in lemmings of the genus Lemmus forms a bilateral morphological module, designated as atypical shape (AF). Three morphotypes of AF have been identified, differing in degree of complexity. The main component of modular variability is an increase in the frequency of individuals with the AF phenotype and the degree of expressiveness of this phenotype with age. Segregation in the offspring into AF and tf individuals in various crossing options does not contradict the hypothesis of monogenic inheritance of these variations. Individuals with the tf phenotype are recessive homozygotes. Sometimes among them there may be undetected heterozygotes. Which phenotype (tf or AF) a heterozygote exhibits may depend on the litter number and (or) on the influence of modifier genes. Dominant homozygotes are considered nonviable.