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 



FIG. 239. The Law of 

 Segregation 



A hybrid individual produces germ 

 cells of two kinds with respect to 

 the character in question, one 

 bearing the elements needed to 

 bring about the development of the 

 dominant character, and the other 

 kind lacking this element. If two 

 individuals, A and , 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 are of two kinds, a% and <? 4 having the factor for dominance, while a^ 

 and <7 2 are lacking in this factor. In the same way, the germ cells given off by B are 

 of two kinds. Now there are four possible combinations of two kinds of eggs with two 

 kinds of sperms : (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. The result is that 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 



