HERITAGE OF THE INDIVIDUAL 



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FIG. 140. Diagram of a Mendelian dihybrid results of crossing yellow 

 round seeded (YR) Peas with green wrinkled seeded (yr). The circles 

 represent the zygotes and the characters of the soma (phenotype) ; the letters 

 within the circles, the germinal constitution (genotype) . The letter groups out- 

 side the recombination square represent gametes. The hybrids of the FI 

 generation are all yellow round seeded since green and wrinkled are recessive. 

 The FI plants form four types of gametes which affords sixteen possible 

 types of zygotes, representing four phenotypes (shown graphically) and nine 

 genotypes (numbered). There is one pure (extracted) dominant (1) and one 

 pure (extracted) recessive (9). The zygotes numbered 4 are identical with the 

 FI generation. Four are homozygotes (1, 7, 8, 9) and the rest are heterozy- 

 gotes. The relative number of individuals composing the phenotypes is 

 9:3 :3 : 1. 



