228 



THE AMERICAN NATURALIST 



[Vol. LI 



metic ratio of 3.9 : 1, or 20.4 per cent, of crossovers. It is 

 evident that the actual results agree very closely with the 

 theoretical expectancy on a 4 : 1 basis of linkage. Indeed, 

 the goodness of fit (Elderton, 1901 and Harris, 1912) is 

 so perfect that x^==.dll, giving a very high value for P. 



TABLE I 



SHO^vI^•G THE Pi Distribution from the Cross 

 C'gRrCC^ y ggrrCc 

 3472 (11) ^3468 (10) " 



From these results it may be said that, at gametogen- 

 esis, the factors of the female parent are so linked that 

 the gametes RG and rg are produced about four times as 

 often as the crossover gametes Rg and rG. Thus far, no 

 evidence is available for demonstrating the linkage of Rg 

 and rG ("repulsion" between R and G). 



Additional evidence on the linkage was afforded when 

 the female parent of the cross and four other plants, in 

 which the R and G factors were heterozygous, were self ed. 

 Each of these plants bore ears with 3 : 1 ratios in aleurone 

 color (total, 1052 purple: 339 colorless). The results ap- 

 pear in Table II. 



Obviously this distribution does not resemble a 

 9:3:3:1 ratio of independent inheritance. The agree- 

 ment between the actual results and the theoretical on a 

 4 : 1 gametic ratio, however, is close^ P being .6733, which 

 is considered a good fit. It may be concluded, therefore, 

 that the factors in these five F^ plants were so linked that 

 R and G occurred together in one chromosome, while r 

 and g were located in the homologous chromosome and 



the purple and the colorless seeds. The proportion should be 1: 1 in this 

 purple and colorless seeds actually planted, often disturbs it. Such a cor- 



