Heredity and Environment 



two contrasting characters in the parents the offspring are di-hy- 

 brids, when three, tri-hybrids, and when the parents differ in more 

 than three characters the offspring are called poly-hybrids. There 

 are certainly few cases in which parents actually differ in only a 

 single character, but since each contrasting character may be 

 dealt with separately, as if it were the only one, and since the 

 number of types of offspring increases greatly when more than 

 one or two characters are considered at the same time, it is cus- 

 tomary to deal simultaneously with only one or two characters 

 of hybrids, even though the parents may have differed in many 

 characters. The different types of developed organisms are called 

 by Johannsen "phenotypes" whereas the different hereditary 

 types whether patent or latent are called "genotypes-" 

 Dihybrids. When two or more contrasting characters of the 



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FlG. 3O. MONOHYBRID DIAGRAM SHOWING RESULTS OF CROSSING ROUND- 



(/?) SEEDED WITH WRINKLED- (W) SEEDED PEAS. Large circles represent 

 zygotes, small ones, or single letters, gametes. In F l all individuals are 

 round but contain round and wrinkled gametes. In F 2 the $ gametes 

 are placed above the square, the $ ones to the left, and the possible com- 

 binations of $ and 9 gametes are shown in the small squares, the relative 

 number of different genotypes being I RR : 2 R(W) :i WW. 



