328 Spotting in Mice and their Genetic Behaviour 



If heterozygous selfs are mated with the " Daruma," four forms of 

 young should be born in an equal proportion. The results thus obtained 

 are indicated as follows : 



Inspecting the data above represented it will be seen that the ex- 

 pectation covers almost the actual results, though the self young appear 

 rather numerously. 



Mating : " Kasuri " x " Daruma." 



If both parents carry the D factor in the heterozygous condition 

 we should expect one-fourth of the young to be homozygous DD mice. 

 But if such young perish in an early stage of ontogeny, as was shown in 

 the cross " Daruma " x " Daruma," the expected ratio would be modified 

 into a 2:2:1:1 of "Kasuri," "Daruma," self, and piebald respectively 

 instead of a 3:1 :3:1, as one of the parents ("Kasuri") carries the S factor 

 in a single dose and another one has invariably the composition of S'S'. 

 The actual numbers obtained from the reciprocal crosses of this sort are 

 represented in the following table : 



The results accord nearly with the expectation based on a ratio 

 2:2:1:1. Thus it reveals, the occurrence of the mortality of the DD 

 carrying embryos in this cross. 



Mating : " Kasuri " x " Kasuri." 



When doubly heterozygous " Kasuri " are mated together, the ex- 

 pected ratio is six " Kasuri," two " Daruma," three selfs and one piebald, 

 as young homozygous for the D factor will have perished before birth. 

 The results obtained from such a sort of cross are shown in the 

 following table : 



In this cross, as the factors dealt with are transmitted independently 

 of each other, four sorts of gametes are produced in equal numbers, 

 namely, lSD:lS'D:lSd:l S'd. These gametes would give nine sorts 



