A number of important gene loci are located in chromosome 1, in which nine gene loci are known to be located, more than for any other cotton chromosome. Genetic information on chromosome 12 and its homeologue, chromosome 6, have previously indicated that le(1) and gl(2) are linked, and that the former, at least, might be located in the long arm of chromosome 12. Only two genes of this chromosome, N(1) and Pgm(1) have been mapped to a chromosome arm. We report herein the results of a mapping experiment aimed at determining the positions of le(1) and gl(2) in chromosome 12. Testcross progenies derived from normal and from monotelodisomic (deficient for the short arm of chromosome 12) F₁ plants were genotyped. Segregation data indicated that both le(1) and gl(2) are indeed located in the long arm. The observed frequencies of recombination suggest respective centromere-locus map distances of 13.2 (±5.5) cM and 29.7 (±7.5 cM). However, the observed recombination frequency between the two loci suggested a gene-gene map distance of 29.7 (±4.8 cM). Thus, the true centromere-gene distances probably differ somewhat from the values suggested by our data. Nevertheless, the loci have been located to an arm, and ordered relative to the centromere. The N(1) locus, which has been mapped previously to 11 cM from the centromere, should be close to the le(1) locus.

This work was supported in part by the Texas Agricultural Experiment Station.