514 TRANSMISSION 



and it aims to predict the character of the offspring when these 

 hybrids are bred together. 



How will this hybrid breed? Will it continue ''pure," or 

 will it break up into its component parts ? This question 

 Mendel's law attempts to answer, and the essence of the law 

 can be stated in two propositions : 



1. When crossed forms, or hybrids (BR}, are bred together, 

 their offspring will not all resemble the crossed parents, but one 

 fourth, or 25 per cent, will be like the original pure parent B, 

 another fourth will be like the other original pure parent R, and 

 one half, or 50 per cent, will resemble the crossed forms, so 

 that the offspring of the cross will tend to assume the original 

 general form of B 2 + 2 BR + R*. Of these the "pure" indi- 

 viduals will breed as true as to the character in question as if 

 their ancestors had never been subjected to crossing ; and the 

 50 per cent of crosses, when bred among themselves, will again 

 split up into pure and crossed forms in the proportion of 1 : 2 : i , 

 so that BR bred with BR will give offspring represented by 

 ip _|_ 2 BR + R 2 indefinitely. In other words, the offspring of 

 hybrids will not all be hybrids, but they will assume the same 

 general proportions that are assumed when pure forms are 

 allowed to breed together indiscriminately. 



If this theory be true, it shows the impossibility of breeding 

 a cross true to its own type, on account of its innate tendency to 

 split up into its original pure or uncrossed forms, a tendency 

 which has long since been encountered by breeders ambitious 

 to fix a fortunate cross, and which has gone far to convince the 

 popular mind of the difficulty in effecting a real cross. 



2. The second fundamental in Mendel's law is the distinction 

 between dominant and recessive characters. If the characters 

 in question were evenly ''balanced," and equally discernible, 

 then in a population like 2 + 2 BR + R 2 the B 2 would be 

 clearly defined, say black. The R 2 would also be clearly defined, 

 say red, and the 2 BR would be some kind of blend or mixture 

 of the two ; in other words, such a population would be easily 

 assorted into three groups in the proportion of 1:2:1. 



On the other hand, suppose one character to be strong and 

 easily noted, as a red color, or a strong, heavy stem, while the 



