FREE INSTITUTE OF SCIENCE 



49 



MENDEL AND HIS LAW 



It is quite evident then that roundness and wrinkledness are very different 

 in their behavior in peas. No one can tell looking at a round pea whether it 

 will always produce round peas. It may be pure bred and may always do so. 

 On the other hand, beneath the roundness there may lie concealed the power 

 inherited from a wrinkled ancestor of producing wrinkled offspring. No 

 wrinkled pea, self -fertilized, however, can produce round offspring. If a pea 

 is wrinkled, its blood in this respect is pure and its descendants will always be 

 pure unless crossed with round peas. Roundness, then, in peas may conceal 

 wrinkledness but wrinkledness cannot conceal roundness. Mendel expressed 

 this by saying that roundness is dominant while wrinkledness is recessive. 



Mendel found that when he planted yellow seeds, he might get only yellow 

 or he might get some yellow and some green seeds, but when he planted green 

 seeds, he always got only green. It is evident here that yellowness in peas, 

 like roundness, is dominant, while greenness, like the wrinkled condition, is 

 recessive. Accordingly, when yellow and green peas are crossed, the first 

 hybrid generation is always yellow, but the second hybrid generation is three 

 yellow to every one green. Of these three yellow, one is pure yellow and two 

 are hybrids, producing both yellow and green descendants in the ratio of three 

 to one. Next he tried crossing peas with brown seed coats with others that had 

 white. He found the brown color dominant and the white recessive and that 

 later generations were produced in just the same proportions as had taken place 

 when round and wrinkled or yellow and green seeds were crossed. 



Some peas have inflated pods; in others the pods get constricted between 

 each pea and the next. Mendel found on crossing these that the swollen pods 

 were dominant over the constricted, the third generation consisting of three 

 swollen to one constricted. He found two other peas that differed in the color 

 of their unripe pods. Some peas when unripe have green pods, while others 

 have pods which are yellow almost from the first. Here coloring was entirely 

 reversed from what he had found it in earlier experiments. In pods, the green 

 color is dominant over the yellow, and in each generation, after a cross, the pro- 

 portion is as three to one. Still another pair of qualities in peas were contrasted 

 by Mendel. Some pea- vines bear their blossoms in the axils of the leaves, while 

 others bear them on the tips of the stems. Mendel found that in this respect 

 the axillary condition was dominant over the terminal and no one could tell, 

 looking at an axillary bush, whether the peas on it would spring into more plants 

 with axillary blossoms or whether they would come terminal, but the peas on a 



