THE CREATION OF SPECIES 



high vine, with white flowers, smooth pods, and 

 wrinkled yellow peas. Another variety would pre- 

 sent some other combination of these various quali- 

 ties. Mendel came to think of the various qualities 

 as "unit characters," susceptible of being transmitted 

 unchanged from parent to offspring. And he pres- 

 ently discovered some very curious facts about the 

 manner of their transmission. He found that oppos- 

 ing characters say tallness versus dwarfness al- 

 ways act in the same way toward each other in 

 inheritance. 



If you cross-fertilize tall-vined and short-vined 

 peas, for example, the hybrids of the first generation 

 will all be tall. In Mendel's phrase, tallness is a 

 "dominant" quality and shortness a "recessive" qual- 

 ity. But if the tall hybrids are now self-fertilized, as 

 is normal with the pea, their offspring will be partly 

 tall and partly short, in proportion of three of the 

 former to one of the latter on the average. And in 

 the next generation, the offspring of this short vine 

 will all be short; the offspring of one of the tall vines 

 will all be tall; and the offspring of the other two 

 tall vines will be partly tall and partly short in the 

 proportion of three to one. 



This formula will be repeated over and over in 

 successive generations. No matter how often the 

 experiment is repeated, the results are always the 

 same: in the first filial generation all the offspring 

 show the "dominant" trait, the "recessive" trait be- 

 ing repressed but not organically obliterated. In 

 the second filial generation, we have one pure dom- 

 inant, like the tall ancestor, one pure recessive, like 



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