THE FATE OF HOMOZYGOUS YELLOW MICE 



133 



occurrence agrees numerically with the requirements of such a 

 case, but a definite proof that such an assumption is vahd must 

 await future experimental inquiries. If it is possible at some 

 future time to transplant the ovaries from a yellow female to a 

 mouse of another coat color, it is conceivable that a subsequent 

 mating with a yellow male might, under the assumed more 

 favorable uterine conditions thus obtained, produce viable homo- 

 zygous yellows. 



The statistical evidence from this research is presented in 

 table 2, where embryos less than three days old are omitted, 

 owing to the failure of abnormalities to become evident before 

 the morula stage. 



TABLE 2 



Showing percentage of degenerate embryos in yellow as compared to ivhite mice 



Total sets of embryos from healthy non-suckling 



females 3 to 20 days pregnant 



Total normal embryos 



Total degenerate embryos 



Percentage of degenerate embryos 



The data show clearly that the degenerate embryos occurring 

 quite regularly in healthy yellow females mated with males of 

 the same coat color must be considered as of a quite different 

 nature from those occasionally found in white mice, for the latter 

 are found almost only, if not invariably, in unhealthy females. 

 The evidence thus strongly indicates that the former are the 

 missing homozygous animals. The proportion of degenerate 

 embryos in normal yellow females is, including additional material 

 obtained since the publication of the preliminary report, 29+- 

 per cent, which is but little higher than the Mendelian expecta- 

 tion of 25 per cent, and is quite within the limits of probability 

 when the total amount of the material is relatively small. 



