258 



HEREDITY AND VARIATION 



OQ 



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characters would be likely to appear in the offspring of the 

 second generation in the ratio of three to one. Such characters 

 as would appear to the exclusion of others in the first crossing of 



the plants were called dominant, 

 the ones not appearing, reces- 

 sive characteristics. When these 

 seeds were again sown the ones 

 bearing a recessive characteris- 

 tic would produce only peas 

 with this recessive characteris- 

 tic, but the ones with a domi- 

 nant characteristic might give 

 rise to a pure dominant or to 

 offspring having partly a domi- 

 nant and partly a recessive 

 character; pure dominants be- 

 ing to the mixed offspring in the 

 ratio of 1 to 2. The pure domi- 

 nants if bred with others like 

 themselves would produce only 

 pure dominants, but the cross 

 breeds would again produce 

 mixed offspring of three kinds 



Illustration of Mendel's Law. .-, , . /. i 



in the ratio of one dominant 

 to two cross breeds and one 



recessive. The feature of this work that interests us is that unit 

 characters are passed along by heredity in the germ ceils pure, 

 that is, unchanged, from one generation to another, and inde- 

 pendently of each other. 



Determiners of Character. A child then resembles his par- 

 ents in some definite particulars because certain determiners of 

 characters have been present in the germ cells of one of the 

 parents. If the determiner of a certain character is absent 

 from the germ cells of both parents, it will be absent in all of 

 their offspring. 



These discoveries of Mendel are of the greatest importance in 

 plant and animal breeding because they enable the breeder to 



