166 



GENETICS IN RELATION TO AGRICULTURE 



the basis of independent segregation of the factors indicates a fairly 

 close correspondence between the two. It may be of some significance, 

 however, that walnut and rose are the deficient classes in both cases. 



From the standpoint of factor interaction this case is of interest 

 because it shows clearly that the character expression of a given set of 

 factors cannot be predicted with certainty from the known character 

 expression of some of these factors. It would have been impossible 

 to predict from the character expressions involved that rose X pea 

 would give walnut-comb fowls or that by recombination of the two 

 recessive factors involved a single-comb fowl would result, for these 

 two new comb types are totally different from the rose and pea types 

 from which they can be derived. The obtaining of new characters of 

 this kind by factor recombination is by no means an unusual thing in 

 genetic experiments, and is sufficient justification in breeding work for 

 testing factor combinations to determine what sort of character ex- 

 pression may result from them. 



CRVH 



CrVH 



cRVH 



crVH 



CRVH 



CrVH 



cRVH 



crVH 



FIG. 77. Ft checkerboard analysis of a cross between two varieties of stocks, white 

 glabrous (ccRRVVHH) and cream glabrous (CCrrVVHH). 



Miss Saunders' Factor System in Stocks. A more complicated case 

 of factor interaction as related to character expression has been in- 

 vestigated by Miss Saunders in stocks (Matthiola) and has been inter- 

 preted in somewhat the following fashion with respect to the factors 

 and factor relations therein concerned. 



C a factor for chromogen base which by itself gives a cream-colored 

 flower. Its allelomorph, c, gives white flowers. 



R a factor for red coloration, epistatic to C. 



V a factor for violet coloration epistatic to R. 



H a factor for the production of hairs on the leaves, active only in the 

 presence of C and R. 



The complicated relations existing between these factors are well 



