INHERITANCE 



185 



V may fertilise V or v. Since the probability of two events 

 happening together is the product of their separate probabilities, 

 the resulting probabilities of all possible combinations are 

 (1)2 VV : (i)2 \v : (1)2 v\ : (i)2 vv. This gives the pro- 

 portions I : 2 : I for pure longs, impure longs, and vestigials, 

 or a 3 : I ratio of longs and vestigials. 



In general characters distinguishing different hereditary 



Vestigial, 



VV 



vv 



Vv 

 Vv 



Vv 



Long-winged. 



Long-winged. 



^/ 



vv P, 

 Vv Fi 



vv F\ 



1 

 Vestigial. 



Fig. 41. — Genetic segregation. 



Strains are distributed in hereditary transmission according 

 to the assumption that they depend upon genes derived from 

 both parents which segregate in the formation of the gametes, 

 so that a gamete either contains the paternal or the 

 maternal gene. The individual bearing dissimilar paternal 

 and maternal genes (heterozygous condition) is not always 

 predominantly like one or the other parent ; it may be quite 

 intermediate, or unlike either. When the character of one 



