Linkage Studies in Gossypium. I. Altered Recombination in Allotetraploid G. Hirsutum L. Following Linkage Group Transference From Related Diploid Species

Abstract

PECIATION among Gossypium species has been suggested to result by S multiple gene substitution and mutation as well as by cryptic structural differentiation of the chromosomes (STEPHENS 1950). Hybrids between species may show no cytological evidence of gross chromosomal divergence, but genetic recombination between linked loci in these hybrids might be expected to differ from that of the parental species due to cryptic structural differentiation of the chromosomes carrying the linked factors. Such a change in recombination has been reported by LODEN (1950) for the red plant-cluster ( R Z -c l ) linkage in G. hirsutum X G. barbadense L. This change was attributed to cryptic structural differentiation of the chromosomes in the hybrid.On the other hand, a reduction in genetic recombination of interspecific hybrids could result from genes having a specific effect on chromosome pairing, particularly those causing a lowered chiasma frequency at metaphase. MENZEL and BROWN (1955) report F, segregation of plants having lowered chiasmata frequencies from an F, G. hirsutum X G. barbadense cross with normal bivalent