The Orientation of Interchange Complexes and Quadrivalents in Gossypium hirsutum and Eu-Sorghum

Studies were made in Eu-sorghum of the orientation of reciprocal translocation chromosomes, and of quadrivalents of hybrids and pure species tetraploids. In all cases segregation was directional and agrees with the hypothesis that if a species displays directed orientation of the chromosomes in an interchange complex at metaphase I, the quadrivalents in an autotetraploid of this species likewise will display directed orientation. But comparable studies in Gossypium hirsutum on the orientation of chromosomes at metaphase I in interchange complexes and in quadrivalents of an autoploid are at variance with the hypothesis. Some interchange chromosomes of G. hirsutum show directed segregation while others behave like the autoploid and do not show directed segregation. Limited data indicate that the type of configurion is determined at the time the centromeres begin repelling one another. The autoploid of G. hirsutum was the result of spontaneous doubling in a normal plant. Modes of association and chiasma frequency per chromosomes in the autoploid are presented. It is concluded that the chiasma frequency per chromosome in the amphidiploid G. hirsutum is between 1 and 1.5.