622 IMPROVEMENT OF LIVING THINGS BY MAN 



show the recessive character. If these peas having the recessive 

 character are crossed with each other in another generation, they 

 will produce all wrinkled peas, the recessive character ; and such 

 peas, when bred again and again with peas of the same kind, 

 will continue to produce wrinkled peas. The recessive character 

 has been segregated out and is now known as an extracted recessive. 



yellow y® 



($)y green 



Smooth ® tz ©r vrtttklect 



Y ^-u*r r$p& ds 



B 



yellov yellow hybrids green 



If peas with yellow seed coats are crossed 

 with peas w.th green seed coats, their off- 

 spring will be yellow hybrids. Yellow is 

 dominant to green in color. If these hybrids 

 are cross-pollinated, the F2 generation will be 

 25 per cent yellow, 50 per cent yellow hybrids, 

 and 25 per cent green. 



R£ Ri~ "dr xt 



Smooth smootfc . ,-wHnklecC 

 taybmdts 



If peas with smooth seed coats are 

 crossed with peas wtih wrinkled seed coats, 

 their offspring will all be smooth-coated 

 hybrids. Smooth is dominant to wrinkled. 

 If these hybrids are then crossed, the F2 

 generation will be 25 per cent smooth, 50 

 per cent hybrid, and 25 per cent wrinkled. 



This shows Mendel's Law of Segregation. Its importance in plant 

 and animal breeding can readily be seen. 



The 75 per cent of F 2 peas which are seemingly all smooth-coated 

 are in reality 25 per cent smooth and 50 per cent mixed, that is, 

 having both characters, the recessive hidden by the dominant. 

 If we can separate the pure dominants, they will produce only 

 dominants, while the mixed hybrids will continue to breed domi- 

 nants and recessives in the ratio of 25 per cent dominant, 50 per 

 cent mixed, and 25 per cent recessives. 



In crossing white rats with black ones black is dominant over 

 white, as is seen in the figure on page 624. But in the F 2 generation, 

 as in the peas of Mendel's experiments, the recessive color is segre- 

 gated out. This law of segregation works so that when pure 

 dominants are mated with hybrids there is a segregation of 50% 

 dominants and 50% hybrids and when recessives are mated with 



