HEREDITY 



447 



further, and this remarkable discovery 

 was made : the green-seeded individuals, 

 whether mated with one another or 

 with green-seeded individuals of the 

 original stock, always produced green- 

 seeded offspring. In other words, al- 

 though they had hybrid parents with 

 yellow seeds, they themselves were 

 pure in the sense that they reproduced 

 or transmitted the green-seeded char- 

 acter to their offspring in exactly the 

 same way as their pure green-seeded 

 ancestors. This principle has been 

 found to hold true in all cases where 

 experiments with plants and animals 

 showing alternative pairs of characters 

 have been carried far enough. An in- 

 dividual of hybrid parentage having a 

 recessive character is called an extracted 

 recessive, or the character in question 

 may be spoken of as the extracted re- 

 cessive. It is just as pure with respect to 

 that character as an organism can be. 



On the other hand, the yellow- 

 seeded offspring of the yellow-seeded 

 hybrids turned out to be of two 

 kinds: (i) those that produced only 

 yellow seeds in subsequent generations, 

 pure like the yellow-seeded ancestor ; 

 (2) those that behaved like their hybrid 



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Fig. 239. The Law of 

 Segregation 



A hybrid produces germ cells of 

 two kinds with respect to a pair of 

 contrasting characters, — one kind 

 bearing the elements needed for 

 developing the dominant character, 

 and the other kind bearing the ele- 

 ments that result in the recessive. 

 If two individuals, A and Z>, both 

 hybrid and both showing the dominant character, are mated, they may give rise to three 

 kinds of offspring. The germ cells given off by A axe. of two kinds, a^ and a^ having 

 the factor for dominance, while (Zj and ao bear the factor for recessiveness. In the 

 same way, B bears two kinds of germ cells. The two kinds of eggs can combine with 

 the two kinds of sperms in four ways: (i) a recessive egg combines with a recessive 

 sperm ; (2) a recessive egg combines with a dominant sperm ; (3) a dominant egg 

 combines with a recessive sperm ; (4) a dominant egg combines with a dominant 

 sperm. As a result, half the offspring are again hybrid and the other half pure- 

 and the pure are likely to be dominants and recessives in equal numbers. Note 

 that the hybrids resemble the dominant grandparent, giving the appearance of one 



recessive to three dominants 



