Parent 2 



Offspring 



MENDEL'S FIRST SURPRISE 



From our common experience we expect offspring to resemble both parents. When 

 Mendel crossed a pure breed of tall plant with a pure breed of dwarf, ail the offspring 

 were tall. When he crossed a pure smooth-seed variety with a wrinkled-seed variety, 

 all the offspring had smooth seeds. The hybrid of hard-pod and soft-pod varieties 

 all had hard pods. The results were the same whichever parent had the special trait 



of breeders, who consistently failed to establish new varieties even where they 

 constantly mated hybrids with similar hybrids. 



Inbreeding of the hybrids yields two kinds of offspring: (1) those with 

 the dominant character and (2) those with the recessive character (see illustra- 

 tion opposite). That is, the two original qualities — green and yellow seeds, for 

 example — reappear. The progeny of the hybrids break up into two types, 

 resembling the two ancestral types. These two types of offspring segregate 

 in the proportion of three dominants to one recessive (3 :1). Inbreeding in 

 the next generation leads to further segregation — a fact which had always 

 confused hybridizers in the past. But here a new fact appears: all the reces- 

 sive green plants in the second hybrid generation breed true, and also some of 

 the dominant yellow. 



Purifying the Mixture The recessives (greens) breed true in every 

 succeeding generation. This is in spite of the fact that they were derived from 

 yellow (hybrid) parents. Such "extracted" recessives are considered "pure," 

 for they always breed true. 



A76 



