LAWS OF HEREDITY 



621 



tall 



short 



Fi 



all tall Ch/brid) 



F2 



different characters. For example, he crossed tall plants with 

 short ones, and smooth peas with wrinkled ones. The results of 

 these crossings showed 

 that these characters 

 are always transmitted 

 to the next generation 

 as units, not as blend- 

 ings of the two oppos- 

 ing characters. This 

 was his first great dis- 

 covery, the inheritance 

 of unit characters. 



The law of domi- 

 nance. But Mendel 

 found, in crossing peas, 

 that the first generation 

 of hybrids 1 always 

 showed a curious result. 

 One character would 

 appear, while its oppo- 

 site would seemingly be 

 lost. If, for example, 

 smooth and wrinkled 

 peas were crossed, the 

 hybrids were all smooth. If tall and short pea plants were bred, 

 the hybrids were all tall, and similar results were obtained with 

 other pairs of characters with which he experimented. This gave 

 rise to the statement that certain unit characters are dominant 

 over others which are called recessive characters. 



The law of segregation. But these recessive characters were 

 not really lost. If some of the hybrid smooth-coated peas are 

 fertilized by others of the same kind and their seeds planted, the 

 next generation (known to breeders as the F 2 generation) will 

 include some pea plants bearing smooth peas and some bearing 

 wrinkled peas, in the ratio of 75 : 25. One quarter of all the peas 



1 Hybrid : a plant or animal that contains a pair of widely different unit char- 

 acters — as smooth and wrinkled skins in peas. 



talUh/brid) talUhybrid) short 





If a tall plant is crossed with a short plant their off- 

 spring (the Fi generation) will all be tall. If these tall 

 hybrids are then crossed, their offspring (the F2 genera- 

 tion) will be in the proportion of one tall, two tall hybrid 

 and one short. 



