304 GERM-CELL CYCLE IN ANIMALS 



separated into two groups ; one, containing on the 

 average one-third of these plants, was pure yellow and 

 homozygous as regards color; the other two-thirds, 

 although yellow, contained green in a latent condi- 

 tion and were therefore impure yellows and "hetero- 

 zygous" as regards color. The conclusion reached 

 was that the eggs and spermatozoa produced by the 

 first (Fi) generation (see Fig. 81) were pure yellow or 

 pure green and that chance combinations during 

 fertilization resulted in the three classes of individ- 

 uals in the second (F 2 ) generation ; that is, one-fourth 

 pure yellow, one-fourth pure green, and one-half with 

 dominant yellow and green recessive. Evidently 

 the factors for yellow and green repulsed each other 

 during the maturation so that they became localized 

 in different germ cells. 



Such a characteristic as the color of the seeds of 

 these peas is known as a unit character, and the sepa- 

 ration of the factors of such a character during 

 maturation is referred to as the principle of segrega- 

 tion. Mendel further discovered that if the seeds 

 were also wrinkled or round, such characters behaved 

 independently of the color characters. These and 

 other experiments described by Mendel opened 

 the way for new lines of investigation which have 

 yielded results of vast importance from the stand- 

 point of heredity and evolution. 1 



Soon after Mendel's results were "rediscovered" 



1 For more detailed accounts of experiments and theories that have 

 been published within the past fourteen years the reader is referred 

 to the books of Bateson (1909, 1913) and Punnet (1911). 



