376 THE POPULAR SCIENCE MONTHLY 



This is written DD and ER, not simply D and E, because we are sup- 

 posing that each individual is pure for the character involved, that is, 

 has received D or E from each parent. 



First filial generation DE X DE X DE X DE, as many as there 

 may happen to be. These are written DE because each gets D from 

 one parent (which has nothing else to give) and of course E from the 

 other. Now in the next generation each parent contributes, not its 

 whole " DE/' but one or the other, according to the laws of chance. 

 Accordingly, DE X DR may produce a DD, or a DE, or a EE, and as a 

 matter of fact, they do so. Why should there be any particular nu- 

 merical proportion? If we put black and white balls in a bag, and 

 draw them out in pairs at random, the chances are equal that we shall 

 get two alike, or two different. It is so with our crosses. The cases in 

 which we get two alike may be of two kinds, both black or both white, 

 or in the case of the crosses, both D or both E. The cases in which we 

 get two different are necessarily alike, black and white, or D with E. 

 Hence, according to the law of chance, we expect in the third genera- 

 tion the following : 



1. Both alike, DD and EE. 



2. Not alike, DE and ED, which are the same. 



Now we have seen that because of dominance E does not show 

 when D is present, so that a DE looks like a DD. Consequently, of the 

 above four cases, three show the dominant character, and one (EE) 

 shows the recessive. The whole diagram may now be reconstructed : 



1. DD X RR (original cross). 



3. DE X DR X DR X DE (first filial generation). 



3. DD X DE X RD X RR (second filial generation, or grand- 

 children). How can this be confirmed? Obviously, if the facts are as 

 here given, the DD and the EE of the third line are now pure, in 

 spite of the fact that the DD had an EE grandparent and a DE parent, 

 and the EE a similarly complicated ancestry. Take a number of these 

 pure types, now called " extracted recessives " and " extracted domi- 

 nants," and breed them separately, the DDs with DDs, and the EEs 

 with EEs, and they will breed irue, and their descendents will forever 

 remain true, unless contaminated by a cross, or some new variation 

 arises. The DEs, however, when bred together, will again produce the 

 " three-to-one " results, just like their parents. Consequently, it is 

 possible to extract a pure strain out of an impure one, a fact of tre- 

 mendous scientific and practical importance. 



Mendel's results were published in Briinn in 1866, but attracted 

 little or no attention. They never became known to Darwin, who would 

 have immediately perceived their importance. In 1884, when Mendel 

 died, no one had the slightest idea that his name would ever be familiar 

 to scientific workers, though Mendel himself used to say " Meine Zeit 



