236 PROCEEDINGS OF THE AMERICAN ACADEMY. 



From the foregoing considerations, we see that it is entirely possible 

 for a breeder, under the conditions stated, practically to eliminate an 

 undesirable recessive character, in a very few generations, merely by not 

 breeding from individuals which manifest that character. This accords 

 with exjierience. There is, however, a much quicker and surer way of 

 accomplishing the desired result, namely, by selection of pure dominants 

 only for breeding purposes. If a dominant individual, when bred to a 

 recessive mate, has produced among two or more offspring no recessive 

 individual, it is probable that the dominant is pure, and if mated to 

 a similar individual will produce no recessive offspring in subsequent 

 generations. 



By means of a few preliminary breeding tests of individual animals 

 or plants the breeder is thus enabled to establish a race of pure domi- 

 nants as early as the second generation following a cross with recessives. 

 A race of recessives which will breed true, may of course be established 

 at any time by mating two recessive individuals. If the Galton-Pearson 

 law were correct, neither of these things would be possible. 



Suppose that the breeder, as is often the case, does not care to take 

 the trouble to establish a perfectly pure race, being anxious to market 

 large numbers of individuals as soon as possible. By merely weeding 

 out the undesirable recessive individuals his race will steadily improve, 

 as indicated by Table III and the diagram on p. 239, D. In the second 

 generation following a cross between pure dominant and pure recessive 

 individuals it will, as we have seen, consist of 75 per cent dominant 

 individuals ; in the next generation it will consist of 88.8 per cent 

 dominants, and so on. 



If the breeder eliminates recessives but once, namely, in the second 

 generation following the cross, the series will be as follows : — 



1st generation 100 % dominants 



2d generation 75 " 



3d generation 88.8 " 



4th generation 88.8 " 



etc., ad infinitum. If he eliminates recessives twice only, namely, in the 

 second and third generations, the race will thereafter continue to contain 

 93.7 per cent dominant individuals, as follows : — 



1st generation 100 % dominants 



2d generation 75 " 



3d generation 88.8 



4th generation 93.7 " 



5tli generation 93.7 " 



