CASTLE. — LAWS OF HEREDITY. 



237 



etc., ad injimtum. Similarly, if recessives are eliminated three times 

 only, the race will be stable at 90 per cent dominants ; and if fonr 

 times, at 97.1 per cent dominants. In general, as soon as sehction is 

 arrested the race remains stable at the degree of purity then attained, pro- 

 vided of course that one form is as fertile as the other, and subject to 

 no greater mortality. 



Such is the law governing the transmission of a dimorphic condition 

 within a race, or, to give the matter a practical bearing, we may call it 



TABLE IV. 

 Hesults of Selectiox for the Character A in the various Generations 



FOLLOWING A CrOSS BETWEEN A PuEE A AND A PuRE B. 



the law governing race improvement, in cases of alternative inheritance, 

 in which one of a pair of characters is uniformly dominant over the 

 other. In cases in which dominance alternates between the two charac- 

 ters A and B (and such cases are probably commoner than is generally 

 suspected) the process of race improvement by elimination of undesir- 

 able individuals progresses at first somewhat more slowly, but ultimately 

 even more rapidly than in the case already discussed. A cross between 

 A and B will, when dominance is alternative, yield offspring 50 per 

 cent A(B), 50 per cent B(A). Selecting for A, that is, breeding only 

 from A(B)s, the next generation will consist of equal numbers of forms 



