242 Experimental Transformation of Species 



remains pure and is called an extracted recessive. Of the 

 dominants derived from hybrid parents, one-third are also 

 pure and are called extracted dominants. 



Combinations of Characters 



Each individual plant or animal presents of course a 

 multitude of characteristics. Mendel went back to find out 

 what happens to the different traits, while his experiments 

 with respect to one selected pair of characters were giving 

 the uniform appearance of dominance, segregation and ex- 

 traction of ancestral types. He conducted another series of 

 experiments in which two pairs of contrasting traits were 

 taken into consideration — for example, tallness and seed 

 color, or seed color and smoothness of seed coat. These ex- 

 periments showed that each pair of contrasting characters 

 produced its dominance in the first hybrid generation and 

 its segregations in the following hybrid generation, quite 

 independently of the other pair. Thus a tall yellow-seeded 

 plant crossed with a dwarf green-seeded plant would yield 

 a hybrid generation in which all the plants were tall and 

 all yellow-seeded, that is, dominant for both characters 

 (Fig. 62). 



In the following generation, produced by self-fertilizing 

 these hybrids, there was segregation for each trait studied. 

 That is, the plants appeared in the ratio of three tails to one 

 dwarf. There were also three yellow-seeded to one green- 

 seeded. There were, however, new combinations, for four 

 distinct types were present, namely, 



(i) tall yellow-seeded, 



(2) tall green-seeded, 



(3) dwarf yellow-seeded, and 



(4) dwarf green-seeded. 



Recombinations have been found by many investiga- 

 tors to hold in animals as well as in plants. Among guinea 

 pigs and rabbits, for example, pigmentation is dominant 



