Duplicate genes for capsule-form in Bursa bursa-pastoris. 



109 



evidence is made available, however, when we breed from the dominant 

 individuals of the third group of F 3 families, namely, from those which 

 are referable to the expected ratio 3:1. This monohybrid ratio indi- 

 cates that one of the duplicate determiners, either C or D, has been 

 omitted, and that the other was heterozygous in the parents of these 

 families. As the omitted gene cannot be reinstated when the dominant 

 members of these families are self- fertilized, there can be no repetition 

 of the 15 : 1 ratio in the F4 or any later generation derived 

 from the 3 : 1 group of families of the preceding generation. Only two 

 kinds of dominant individuals may be supposed to occur in any one of 

 these families, those which are homozygous and those which are hetero- 

 zygous for the single remaining gene, and the F4 families derived by 

 selfing these individuals should likewise be of but two kinds, containing 

 either nothing but bursa-pastoris, or bursa-pastoris and Heegeri in the 

 ratio 3:1. The 39 families included in the following table were all 

 produced by selfing a like number of bursa-pastoris plants in family 

 No. 09284 recorded in the third section of Table II. 



Table IV. 



A second sowing from same lot of seeds that produced the preceding family. 



