Metaphase I configurations of the reciprocal translocations in a cytogenetic tester set of Gossypium hirsutum L

Twenty reciprocal translocations of the cytogenetic tester set of G. hirsutum were cytologically characterized. Nineteen of the 20 heterozygous translocations had a modal chiasma frequency of four per quadrivalent, 14 of which formed predominantly ring multivalents without interstitial chiasmata and five usually formed ring multivalents with at least one interstitial chiasma at MI. The remaining translocation averaged 3.27 chiasmata per quadrivalent and oriented predominantly as an alternate chain. Ten of the 20 reciprocal translocations formed predominantly alternate orientations at MI. Eight of these 10 lines were reciprocal translocations between two large A subgenome chromosomes. This suggests that the large A subgenome chromosomes allow the quadrivalent to be more flexible, resulting in easy reorientation to the stable alternate configuration. The constraints imposed by the chiasmata within the chromosome arms also appear to influence the orientation of the centromeres in quadrivalents at MI. Lines, In which a high frequency of multivalents with interstitial chiasma were observed, had a significantly lower frequency of multivalents with either one or two centromeres not involved in spindle attachment or with 3:1 orientations.