Protein variation in strains of mice differing in body size

Abstract

SUMMARY Nine (41%) of the 22 enzymic and non-enzymic loci examined in a strain of mice divergently selected for six-week body weight (six lines selected in each direction and six controls) were found to be polymorphic. The degree of polymorphism varied between the replicates from a maximum of 38% to a minimum of 14% with an average individual heterozygous at 7·7% of its loci. There was no obvious association between any of the isozyme variants and body size. The frequency distribution among the 18 lines was adequately accounted for by random genetic drift. However, an association was observed between body size and the Hbb locus; the Hbb s allele was found to be fixed in all of the six Large lines. An examination of the variance of gene frequencies at this locus excluded random genetic drift as an explanation for the fixation.