LINKED QUANTITATIVE CHABACTEES IN 

 WHEAT CROSSES 



DR. GEORGE F. FREEI^IAN 

 Arizona Agricultural Experiment Station 



Since wheat has but 8 chromosomes in the sexual cells 

 and since the parents in the macaroni bread wheat crosses 

 here discussed certainly differ in more than 8 visible char- 

 acters, it was thought likely that a genetic linkage of 

 some of these might be found. The following study is an 

 endeavor to discover whether or not there is such a link- 

 age between the shape of the head, i. e., ratio of width of 

 head (measured parallel to the face of the head which 

 shows the sinuous furrow formed between the two rows 

 of spikelets) to the thickness (measured parallel to the 

 array of seeds in the spikelet) and the texture (trans- 

 lucency or opaqueness) of the grain. Of the two parents 

 here discussed No. 1, the macaroni wheat, had a much 

 flattened head and very hard translucent grains, whereas 

 the other parent. No. 35 (a bread wheat), had a nearly 

 square head with soft opaque grain. 



The seed on the Fj plants of this cross were all wrinkled 

 and intermediate in texture between the two parents, i. e., 

 they were dull, being neither translucent like the macaroni 

 parent nor opaque like those of the bread wheat parent. 

 In order to make a quantitative expression of hardness 

 the perfectly translucent grains of the macaroni parent 

 were called 100 per cent, hard, the seeds of the 50 per 

 cent, hard and those of the bread wheat parent were 

 called per cent. hard. Since in the seeds of the Fo and 

 F3 plants every possible degree of intergradation oc- 

 curred between the characters of the two parents and 

 since any form of classification adopted would be purely 

 arbitrary, it was decided to make it the most simple pos- 

 sible and place all of the variants into three groups by the 

 following means : a grain that was approximately as hard 

 683 



