LINKAGE RELATIONS IN MEN DELI SM 



105 



tution of the hereditary material and of the operation of the chromosome 

 mechanism in the distribution of the hereditary units. 



Purple Aleurone and Waxy Endosperm in Maize. A typical example 

 of the relations which obtain for linked factors is given in the experiments 

 which involve purple aleurone color and waxy endosperm in maize. We 

 have shown in Chapter V that aleurone color in maize in certain cases 

 depends on a single factor difference, so that in F z segregation is in the 

 ratio 3 purple : 1 white. For waxy endosperm, when contrasted with 

 starchy endosperm, Collins has shown that starchiness is dominant and 

 that in F z segregation is in accordance with the normal monohybrid 

 ratio, 3 starchy : 1 waxy. The factors involved in these two cases are 

 C for aleurone coloration and its recessive allelomorph c for colorless 

 aleurone, and W for starchy endosperm and its recessive allelomorph 

 w for waxy endosperm. Collins found that when purple starchy corn, 

 CCWW, is crossed with white waxy, ccww, Fi is purple starchy, CcWw; 

 but ^2 does not segregate in the expected dihybrid ratio 9 purple starchy: 

 3 purple waxy : 3 white starchy : 1 white waxy. The data which he 

 actually obtained from six ears are given in Table XIX. The calculated 



TABLE XIX. F z SEGREGATION OF CROSS PURPLE STARCHY X WHITE WAXY 



(After Collins) 



ratio based on independent segregation evidently falls far short of agree- 

 ment with the observed results, even though, when each pair of characters 

 is considered separately, the agreement with the monohybrid ratio is 

 very satisfactory. Thus for purple and white the observed totals are 

 2037:699 giving a ratio of 2.98:1.02, and for starchy and waxy the 

 observed totals are 2053:683 giving a ratio of 3.00:1.00. The latter 

 ratio is so close that it would be perfect if only one kernel were shifted 

 from the starchy to the waxy class. Taking each pair separately, there- 



