Genetic and phenotypic relationships between ovulation rate and body weight in the mouse

Abstract

SUMMARYThe genetic and phenotypic regressions and correlations between ovulation rate and body weight were examined in a random bred strain (Q) of laboratory mice during the course of three experiments. These experiments were (1) a sib analysis; (2) selection for natural and induced primiparous ovulation rate; and (3) replicated selection for 6-week weight. The following results were obtained:(a) The genetic correlations between body weight and natural and induced ovulation rate were positive, and approximately equal to 0·4 and 0·6 respectively.(b) The genetic regressions of natural and of induced ovulation rate on body weight were approximately 0·4 and 0·9 eggs per gram respectively.(c) The genetic regressions of body weight on natural and on induced ovulation rate were approximately 0·5 and 0·25 g per egg respectively.(d) The phenotypic correlation between natural ovulation rate and body weight was approximately 0·4 and the corresponding regression of ovulation rate on body weight approximately 0·4 eggs per gram.(e) The phenotypic correlation between induced ovulation rate and body weight declined from 0·4 at 6 weeks of age to zero at the time of scoring, the corresponding regressions of ovulation rate on body weight declining from 0·1 eggs per gram to zero.It was concluded that natural ovulation rate itself, and both its components (FSH activity and ovarian sensitivity) are positively genetically correlated with body weight. Furthermore, the observation that large mice shed at least as many eggs as small ones in response to the same dose of PMS showed that the response was more closely related to the absolute dose than to the resultant concentration.