Genetic analysis of inferior nurturing ability in RR mice

Females of the inbred mouse RR strain have a limited ability to nurture their offspring, and frequently the young die during rearing. Quantitative trait locus analysis was carried out on the F 2 progeny produced from a genetic cross between RR and KK, a strain of normal nurturing ability, to elucidate the putative genetic basis governing certain aspects of the inferior nurturing ability in the RR strain. One hundred and ninety-two F 2 female mice were mated with C57BL/6J males. After the number of newborns was adjusted to six per dam, nurturing ability was evaluated on the basis of litter weight at days 7, 12 and 21 after parturition. The results showed that 147 of the 192 F 2 dams were able to rear all six pups, although the litter weight varied considerably among litters. Significant evidence for linkage was identified on chromosome 5 near the microsatellite marker of D5Mit161 for litter weight at 12 days after parturition. The R allele (RR strain) at this locus was recessive to the K allele (KK strain), and reduced the litter weight. It is suggested that this locus is one of the heritable components that determine the inferior nurturing ability of RR mice.