MENDEL'S LAW OF HEREDITY 



dividuals of this generation are of two sorts, 

 - B B and B W in character. The B B indi- 

 vidual is pure, so far as its breeding capacity 

 is concerned. It can form only black (B) 

 gametes. But the B W individuals may be 

 expected to breed exactly like the cross-bred 

 blacks of the previous generation, forming 

 gametes, half of which will carry B, half W. 

 Experiment justifies both these expectations. 

 The test may readily be made by mating the 

 black animals one by one with white ones. 

 The pure (or B B) black individual will pro- 

 duce only black offspring, whereas those not 

 pure, but B W in character, will produce off- 

 spring half of which on the average will be 

 black, the other half white. These two kinds 

 of dominant individuals obtained in the second 

 generation from a cross we may for conven- 

 ience call homozygous and heterozygous, fol- 

 lowing the convenient terminology of Bateson. 

 A homozygous individual is one in which like 

 characters are joined together, as B with B; 

 a heterozygous individual is one in which unlike 

 characters are joined together, as B with W. 

 It goes without saying that recessive individ- 

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