330 



HEREDITY 



His paper was received in silence and soon forgotten. In 1900, 

 sixteen years after his death and thirty-five years after his dis- 



The Punnett square may be used to show the possible sorting out during maturation of germ 

 cells of dihybrids and the various combinations resulting after fertilization. Each square repre- 

 sents an individual. This square shows the possible combinations of genes in the nature of 

 guinea pigs of different colors and types. The dominant characters are, large B, representing a 

 pigmented coat, and R, rough hair. The recessive characters are, b, denoting white coat, and 

 r, smooth hair. 



coveries, three other scientists working independently arrived at 

 the same conclusion. JNIendel's work was then given full credit. 



Since 1900, it has been proven again and again that heredity is 

 frequently shown in animals exactly as in INIendel's peas. If pure 

 black guinea pigs are crossed with pure white guinea pigs, all the 

 resulting hybrids will be black, showing black to be dominant. 



The guinea pig and garden peas show^ complete dominance. 

 The Andalusian fowls and four-o 'clocks, in which the characters 

 blend, show incomplete dominance. 



Summary. 1. A pure character is one that gives rise only to a 

 character like itself. The plant or animal possessing it carries pairs 

 of like factors ; for example, two factors for height, one paternal and 

 one maternal. 



2. A plant or animal is a hybrid when it carries a pair of contrasting 

 factors. For example, hybrid tall carries both tallness and shortness. 



