Plants of allotetraploid cotton, Gossypium hirsutum L. (2n = 4x = 52), which are monosomic for chromosome 9 or haplodeficient for the long arm of the chromosome, an Ah genome chromosome, produce a high frequency of aneuploid progeny. The aneuploids include monosomes, trisomes, and multiple monosomic and trisomic combinations that are the result of chromosome nondisjunction, which is induced by the deficiency of the long arm of chromosome 9. Loss of chromosomes occurs far more frequently than additions, and chromosomes of the Ah genome undergo nondisjunction at a significantly greater rate than do chromosomes of the Dh genome. Stained paraffin sections of ovules at different stages of development of monotelodisomic 9 and normal plants (TM1) were analyzed to determine the time and probable causes of nondisjunction during megasporogenesis. The most significant difference between mono 9 and TM1 was observed in ovules in stages of development just before and at the time of flowering. The mono 9 female gametophytes had supernumerary nuclei, indicating that chromosome nondisjunction occurs at the mitotic divisions of the embryo sac.Key words: chromosome nondisjunction, aneuploids, megasporogenesis, cotton, Gossypium hirsutum cytogenetics.
Molecular evolution at homoeologous loci in allotetraploid cotton (Malvaceae: Gossypium hirsutum L)