Duplicate genes for capsule-form in Bursa burs/i-pastoris. 



101 



actujil results of the experiinents. Tlie preniis(^ that doiiiinance is com- 

 plete fixes the character of the Fi which will be uniform aud indistin- 

 guishable from the dominant parent. The expectation in F> and Fa in 

 the case of a dihybrid will be rendered clear by a careful study of the 

 checker-board shown in Figure 4. Since the recessive character can 

 appear only when all the dujjlicate genes are absent, the number of 

 such genes involved in the given cross determines the ratio of dominant 



Q 

 1 



CD 



Cd- 



cD 



cd- 



(f 



CD 



i 



CD . CD 



I : 



Cd . CD 



D . CD 



d . CD 



15 : I 



Cd 



1 



/ ; 



I : 



cD . Cd 



15:1 



■d .Cd 



3 : I 



cD 



1 



CD . cD 



I : 



Cd . cD 



15:1 



I : 



cd . cD 



I 



CD 



Cd . cd 



cD . cd 



3 : I 



■d . cd 



: I 



Fig. 4. Checker-board diagram to visualize the geuetic relations in a dihvbrid Fj family 

 of Bursa bursa-pasloris X Heegeri, in respect to tlie oapsule-cliaracters. The capsules figured 

 in each square indicate by their outline their phenotype, and by their oblique ruling 

 their genotype, the gene C being represented by lines from upper right to lower left, 

 and D from upper left to lower right. Homozygotes are densely lined, heterozygotes 

 more sparsely. The ratios indicate the expectation in Fj when a plant having the 

 genotypic constitution indicated in the same square, is self-fertilized. 



