66 EVOLUTION AND GENETICS 



produce. The pink J^i hybrid four o'clock, that is 

 intermediate, in a sense, between the white- and tlie 

 red-flowered parents produces only white- and red- 

 bearing germ-cells; and the yellow Fi hybrid pea, 

 w^hose color is exactly that of one of the parents, also 

 produces two kinds of germ-cells in equal numbers, 

 yellow- and green-producing. It is obvious from this 

 that the character of the individual is not a reliable 

 index of its ancestry, or of what it transmits to the 

 next generation. 



MendeVs Second Law 



Besides his discovery that members of each pair 

 of elements disjoin in the germ-cells of the hybrid 

 (law of segregation) Mendel made a second dis- 

 covery (the law of free assortment) which also has 

 far-reaching consequences. The following case il- 

 lustrates this second law. 



If a pea that is yellow^ and round is crossed to one 

 that is green and wrinkled {jig. 24), all of the off- 

 spring are yellow and round. Inbred, these give 9 

 yellow-round, 3 green-round, 3 yellow-WTinkled, 

 1 green- WTinkled. All the yellows taken together are 

 to the green as 3:1. All the round taken together 

 are to the wrinkled as 3:1; but some of the yellows 

 are wrinkled and some of the green are round. There 

 has been a recombination of characters, w^hile at the 

 same time the results, for each pair of characters 

 taken separately, are in accord witli ]Menders Law 



