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HEREDITY 



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called the dominant character. The second quality, the one that 

 does not show, although it is actually present, is known as 



the recessive character. 

 Whatever there is in the 

 protoplasm that pro- 

 duces the recessive qual- 

 ity, it is not destroyed 

 in the crossing, for, as 

 shall be seen, the quality 

 may reappear in later 

 generations. In the ex- 

 ample given, the domi- 

 nant traits were tall 

 plants, smooth seed, and 

 yellow seed coats. The 

 recessive traits were 

 short plants, wrinkled 

 seeds, and green seed 

 coats. The individual 

 resulting from a cross of opposite characters is called a hybrid. 

 For example, when plants with yellow seed coats are crossed with 

 those with green seed coats, the offspring appear yellow. Because 

 one of the parents had green seed coats the protoplasm of the 

 offspring must be different. These yellow offspring are hybrids 

 since they conceal the character determined for green. In all 

 external appearances, hybrids resemble pure dominants. 



Mendelian Law of Segregation. Although the tall descendants 

 of a mixed parentage, that is, a tall and a short, may appear tall 

 like one of the parents, its protoplasm or part of its protoplasm 

 is really different. This must be true since it has been built up 

 in part from the protoplasm of the short parent. In the same 

 way, the plant with the yellow seed coat of mixed parentage may 

 resemble, in seed coat color, one of the parents, but it is still a 



When pollen from a pea plant that produces smooth seeds 

 is transferred to a plant that produces wrinkled seeds the 

 resulting plants will produce smooth seeds. In peas, 

 smooth seed coat dominates a wrinkled seed coat. The 

 resulting offspring are hybrid, for when they are self- 

 pollinated their offspring show 75 per cent smooth seeds 

 and 25 per cent wrinkled seeds ; of the 75 per cent smooth 

 seeds, 25 per cent is pure bred smooth, and 50 per cent is 

 hybrid smooth. This illustrates complete dominance, be- 

 cause smooth seed coat completely dominates wrinkled 

 seed coat and does not blend with it. 



