Genetic Correlation between Growth Rate and Litter Size in Mice.

UANTITATIVE geneticists have long been aware that correlated responses Q are common in populations under different types of selection. The primary implication of a correlated response is that the character under selection is genetically correlated with another character, though other parameters affect the magnitude of the correlated response. In the course of selection for a single trait, other than a trait pertaining to reproduction, for an extended period of time, one expects sooner or later to encounter a decline in fertility or net reproduction, This has been reported by WIGAN and MATHER (1942), MATHER and HARRISON (1949), ROBERTSON and REEVE (1952), CLAYTON, MORRIS and ROBERTSON (1957) and LERNER (1958). The purpose of this paper is to report on the correlated response of litter size to recurrent selection for post-weaning growth in an experimental population of mice. MACARTHUR (1949) and FALCONER (1955) have both reported increases in litter size associated with selection for large body size and decreases in litter size associated with selection for small size in mice.