Pure Strain Mice Born to Hybrid Mothers Following Ovarian Transplantation

It is well established that many characters in mammals are affected by naturally occurring variation in the uterus or, to use a more inclusive term, the prenatal maternal environment.Although this factor is regarded as environmental as far as the embryo is concerned, it is itself presumably sub- ject to both environmental and genetic factors (Russell').The work of Wright,2 Wright and Chase,3 Green 4 and others,' who made statistical analyses of variation within inbred strains of mammals, clearly shows that the characters which they studied, polydactyly, white spotting, number of vertebrae, etc., were affected by environmentally determined variation in the prenatal maternal environment.The effect of genetically determined variation in the prenatal maternal environment on character variation has, however, received little attention, perhaps because of a lack of easy methods of evaluating it.Evidence that this factor may be important is provided by the increasing number of cases in which a difference has been observed between reciprocal F1 hybrids ob- tained by crossing inbred strains.Russell and Green6 have reported one -such case for number of lumbar vertebrae in mice.