DETERMINATION OF THE NUMBER AND DOMINANCE RELATIONSHIPS OF GENES ON SUBSTITUTED CHROMOSOMES IN COMMON WHEAT, TRITICUM AESTIVUM L.

A study of awning, culm colour and reaction to pseudo-black chaff in crosses of seven different substitution lines with Chinese Spring wheat was made to illustrate a method that permits the determination of the number and dominance relationships of genes on a substituted chromosome governing a particular character. F2 and F3 results in each of the seven crosses showed that each of the substituted chromosomes carries one gene affecting the character under investigation. On the basis of F1 results, genes for apical awning on chromosome III of Thatcher and Timstein and IV, XII and XXI of Thatcher were found to be recessive; Hope possesses a dominant gene for purple culm colour on chromosome VII and a recessive gene for susceptibility to pseudo-black chaff on chromosome III. Chinese contains alternative alleles for all these genes. A study such as outlined in this report must supplement the study of substitution lines to provide a complete genetic analysis of the character under investigation. The reasons for a supplementary study as well as the advantages and disadvantages of the substitution method in comparison with other methods of analysis are discussed.