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FOUNDATIONS OF BIOLOGY 



crossing, for example, a Pea producing yellow round seeds 

 with one producing green wrinkled seeds. The plants in the 



Key to Symbols 



= Dark 

 O = Light 

 3 = Curly 



= Straight 



FIG. 141. Scheme to illustrate the heredity of human hair characters. Mendelian 

 dihybrid. Dark and curly, dominant characters; light and straight, recessive charac- 

 ters. The arcs represent somatic cells of four individuals. The dominant characters are 

 placed on the outer side of the cells, since they represent the visible characters (pheno- 

 type). The gametes are placed within the arcs (cf. Fig. 142). (From Walter.) 



FI generations bear only yellow round seeds, and therefore 

 yellow and round are each dominant characters when paired 

 with green and wrinkled. After self-fertilization such 

 hybrid plants produce offspring (F2) with seeds showing all 

 the possible combinations of the four characters, and in the 



