The genetic relationship between the Hbb locus and body size in a population of mice divergently selected for six-week body weight.

Abstract

Both pleiotropy and linkage were examined as possible explanations for the fixation of the Hbb3 allele in the six Large lines of a population of mice divergently selected for six-week body weight (six replicates in each direction and six controls). A survey of over 1200 individuals in the lines still segregating at the Hbb locus excluded pleiotropy as a possible explanation. The results showed a nonsignificant effect of haemoglobin genotype on body weight. The linkage relationship of the Hbb locus was examined using a backcross mating system. The Hbb3 c+ region (chromosome 7) of a Large line was backcrossed into its corresponding Small line (Hbb4 c). The resultant difference in body weight between the two segregants (Hbb8 c+ [Hbb4 c; Hbb4 c/Hbb4 c) was measured. The results suggested linkage as the most plausible explanation for the fixation of the Hbb4 allele in the six Large lines.