THEORY AND PRACTICE 



four, on the average, of the progeny of the next 

 generation. And it is observed that the short vine 

 in which the recessive factor thus again makes 

 itself manifest will breed true to shortness, the 

 factors for tallness apparently being altogether 

 eliminated from its germ-plasm. 



Meantime, as just noted, for every short vine of 

 this second filial generation there are three tall 

 ones; and further breeding tests will show that, 

 while these three vines look just alike, there are 

 fundamental differences in their germ-plasm ; for 

 one of them will breed true to tallness (being a 

 pure dominant, as the saying is), while the other 

 two are " mixed dominants" and will have 

 progeny of which, in each group of four, one will 

 be short (pure recessive), one tall (pure dom- 

 inant), and two also tall but of mixed germ-plasm 

 like their parents. 



The essential point is simply that any char- 

 acter that acts as recessive in the Mendelian sense 

 will be seemingly eliminated in the first-genera- 

 tion cross that brings it in combination with the 

 opposite character; but that the recessive char- 

 acter will reappear in the next generation, and 

 will then breed true. So when you find that you 

 are dealing with a recessive quality, you may fix 

 it in the third generation without difficulty. But 

 the dominant quality, on the other hand, although 

 it makes itself manifest in all the first-generation 

 progeny, and in three out of four of the second- 

 generation progeny, has to meet the masked 

 rivalry of recessive factors in two out of three 



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