GENERAL ZOOLOGY 



Females 



Males 



Fig. 6.10. Results of crossing a white-eyed female Drosophila with a red-eyed male (cf. 

 Fig. 6.18). The X-chromosomes and the symbols for the genes are explained in the legend of 

 Fig. 6.9, which shows the reciprocal of this cross. (Modified from T. H. Morgan et al., The 

 Mechanism of Mendel lan Heredity, copyright 1922 by Henry Holt and Co., printed by permission.) 



the cells of a hybrid individual and even though one factor is without effect 

 in the presence of the other. When a hybrid produces its reproductive cells, 

 these two allelomorphic factors, or alleles, one for each of the visible expressions 

 of the character under consideration, must be able to undergo segregation 

 from one another and occur alone in different reproductive cells. When 

 random combination of gametes occurs to form individuals of the next genera- 

 tion, new combinations of genes occur which condition the characteristic 

 ratios of mono-, di-, and trihybridization experiments. The details of the 



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