132 GENETICS IN RELATION TO AGRICULTURE 
of their lack of chlorophyll. Those green plants of the genetic constitu- 
tion Gg when self-fertilized produce grains one-fourth of which again 
give albino seedlings as in the previous generation. The green plants 
of the genetic constitution GG, however, since they are homozygous for 
the factor G produce nothing but green plants in succeeding generations. 
Fre. 58.—Disturbance of phenotypic ratio by a recessive sex-linked lethal factor. Com- 
pare with Fig. 36. 
Morgan has demonstrated the existence of a number of lethal factors 
in Drosophila. These factors result in the death of the individuals at 
some time before they reach the adult stage. They are particularly 
found among sex-linked factors, because sex-linked recessive factors 
have no normal allelomorphs in the male. The results of the presence 
of sex-linked lethal factors is shown diagrammatically in Fig. 58. As 
in corn, the strains are propagated by means of heterozygous individuals. 
Since such individuals can only be females in the case of sex-linked 
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