Volume IX MAKCH, 1920 No. 4 



THE GENETICS OF THE DUTCH KABBIT— 

 A CRITICISM. 



By R. C. PUNNETT. 



(With two Text-figures and Plate XI.) 



In the earlier days of Mendelian studies attention was naturally 

 focussed upon characters which were clean cut, and offered simple 

 material wdth which to test the validity of the principle of segregation. 

 But even in those days there was plenty of evidence for the existence of 

 cases in which a cross between two true-breeding strains led to the pro- 

 duction of a series of forms in F^, ranging between the two extremes 

 characteristic of the parental types. Under peculiarly favourable circum- 

 stances it was found possible to frame an interpretation on strictly 

 factorial lines, involving but a small number of factors. The pigmenta- 

 tion of the Silky fowP was a case in point, analysis shewing that the 

 apparently continuous range fiom the unpigmented to the fully pig- 

 mented condition could be interpreted in terms of three factors only, 

 viz. (1) a factor for pigmentation, (2) a factor for pigment inhibition, 

 and (3) the sex factor, which in the female operates to produce a some- 

 what higher grade of pigmentation than in the male of corresponding 

 genetical composition. Owing to the diverse nature of the three 

 factors the analysis of a continuous series was here much simplified, 

 since specific tests of the factorial interpretation could be readily de- 

 vised and carried out. Many cases, however, present greater difficulties 

 to analysis, because we have no grounds for supposing that there is 

 a qualitative distinction between the various postulated factors. For 

 example, in dealing with the inheritance of size or weight, we may 

 encounter cases where the F2, generation is composed of a series passing 

 imperceptibly from the one extreme to the other. As a typical instance 

 may be cited that of the Hamburgh x Sebright cross in poultry, of 

 which an account was given in the earlier pages of this Journal. It is 

 possible, as was there pointed out, to bring such cases into line with the 



1 Bateson, W., and Punnett, R. C, Journ. Genet. Vol. i, 1911. 

 - Punnett, R. C, and Bailey, P. G., Journ. Genet. Vol. iv, 1914. 



Journ. of Gen. ix 20 



