Genes and Cytoplasm 319 



upon a single pair of alleles, the expression seems to be delayed 

 one generation. Apparently left-handed (sinistral) coiling is 

 recessive to right-handed (dextral). Let us use I to designate 

 the gene for left-handed coiling and L the gene for the right- 

 handed type. 



In the cross LI X H (dextral female X sinistral male), half the 

 offspring are LI and half are II. They are all coiled dextrally, 

 however, because their type of coiling was initiated under the 

 influence of the cytoplasm of the egg from which they were 

 produced, and this egg, in turn, had developed under the influ- 

 ence of the genotype of their mother. Similarly, if a sinistral- 

 type female is crossed with a homozygous dextral-type male, 

 the offspring are all LI; but they all coil to the left because they 

 started to coil in that direction very early in ontogeny under the 

 influence of the cytoplasm of the egg produced in a snail which 

 was homozygous for gene I. Thus in the cross II X LL, the Fi 

 are sinistral but LI, all the r2 are dextral, and the Fs segregate 

 into a 3 : 1 ratio. The particular type of coiling does not indi- 

 cate the genotype of the individual but does show the genotype 

 of its mother. 



