THE NATURE AND EXPRESSION OF MENDELIAN FACTORS 141 
typically different. Of the nine purples, only one breeds true in F;, 
and of the remaining eight purples, four give families which segregate 
in the ratio of 3 purple: 1 white, and four give families showing segrega- 
tion in the ratio of 9 purple:7 white. All the whites, although of different 
genotypes, produce entirely white families. All these relationships are 
shown clearly in the checkerboard. 
In Drosophila a large number of similar cases of like somatic effect 
have been found to be dependent upon different factors. Here the 
linkage values of the different factors with other factors have been 
determined very precisely, and moreover the mutants have for the most 
part arisen directly from the cultures, so that the relationships have 
been established much better than in any other form. 
CP Cp cP cp 
CCRP CCPp CcPP. CcPp 
CP Purple | Purple Purple Purple 
1:0 | 3:1 3:1 9:7 
CCPp | CCpp CcPp Cepp 
Cp Purple White Purple White 
3:1 | 0:1 9:7 | 0:1 
CoPP. | CcPp ccPP |  ccPp 
ce Purple Purple White White 
3:1 9:7 0:1 | 0:1 
| 
CcPp Cepp ccPp | ccpp 
cp Purple White White | White 
9:7 | 0:1 0:1 0:1 
| | 
Fic. 64.—Checkerboard of F2 of cross white (ccPP) *& white (CCpp) maize, showing 
phenotypes and F; segregation as well as genotypes. 
For body color at least three similar mutant factors result in almost, 
identical darker forms. The first of these to be discovered was the black 
* factor which is located in the second group of factors. The factor for 
ebony body color is in the third group, and sable is a sex-linked factor. 
Although so nearly alike that a mixed population could not be certainly 
classified these particular races do show slight differences in coloration. 
Similarly nearly identical results are obtained from three different 
jaunty factors which cause the wings to turn up at the ends. Morgan 
has also pointed out other such similarities in effect of different factors 
which affect eye and wing characters, color, etc. 
Sometimes a dominant and a recessive factor give identical pheno- 
typic results. For an illustration of this we may again turn to aleurone 
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