Cytological studies in cotton

Abstract

1.Gossypium Davidsonii (n = 13), a wild species from California, has smaller chromosomes thanG. Sturtii (n = 13), a wild species from Australia. This difference in chromosome size is maintained in the hybrid, and enables a distinction between the paternal and the maternal chromosomes to be made. 2. The chromosome pairing in the hybrid is incomplete, but allosyndesis takes place about nine times more often than autosyndesis. Univalents are just as frequent between the small chromosomes fromG. Davidsonii, as between the larger chromosomes fromG. Sturtii. 3. The chiasma frequency is the same in the pure species despite the difference in chromosome size. Contrasted with the pure species, the chiasma frequency in the hybrid is significantly smaller in the bivalents containing aDavidsonii and aSturtii chromosome. 4. The difference in the size of the chromosomes of the species under observation is in all probability neither the result of genetic factors, nor associated with a difference in pairing blocks.