Duplicated linkage groups in cotton

The Yg1 duplicate allele for yellow-green was found to be linked with the R1 locus of the D genome of allotetraploid G. hirsutum. The estimate was 20 percent, as was the estimate given for R2-Yg2 linkage on the A genomes (Stephens 1955). The Dw locus was calculated to show linkage with R1 of ca. 27 percent. These loci extended the D genome linkage group to four loci, R1-c11-yg1-dw, the ‘duplicates’ of those reported for the A genome linkage group, R2-cl2-yg2-Lc1-n. The gene order is not necessarily duplicated in both linkage groups. Either of the linkage groups may be useful in three-point linkage tests and the genetic data should be related to the question of chiasmata frequency and position within Gossypium.