no 



PROBLEMS OF GENETICS 



owing to defective constitution (e. g., the albinos of Antirrhinum 

 studied by Baur, and the homozygous yellow mice). I am 

 rather inclined to suppose that in these examples of hybrids 

 breeding true we shall find a state of things comparable with 

 that to which we formerly applied the terms " coupling" and 

 "repulsion." In these cases certain of the possible combinations 

 of factors occur in the gametic series with special frequency, 

 being in excess, while the gametes representing other combina- 

 tions are comparatively few. In a recent paper on these cases 

 Professor Punnett and I have shown that these curious results 

 vary according to the manner in which the factors are grouped 

 in the parents. If A and B are two factors which exhibit these 

 phenomena we find that the gametic series of the double heterozy- 

 gote differs according as the combination is made by crossing 

 ABXab, or by crossing AbXaB. In a normal Mendelian case 

 the FI form, AaBb, produces gametes AB, Ab, aB, ab, in equal 

 numbers; but in these peculiar cases those gametes which contain 



Gametic series 



Nature of zygotic series 



AB 



Ab 



aB 



ab 



i 2ni n 2 2w 



