The Journal of Heredity 1985:76(5):387-389
© 1985 The American Genetic Association 76:387-389
other |
Typical meiotic nondisjunction and its consequences in Coix gigantea
The authors are, respectively, reader and senior research fellow, Unit of Cytogenetics, Department of Botany, Marathwada University, Aurangabad, 431 004, India. They are grateful to Professor R. M. Pai for interest and facilities. One of them (SSB) also thanks the Council of Scientific and Industrial Research, New Delhi for a fellowship.
Abstract
Cytological evidence for typical meiotic nondisjunction is provided for the first time showing 9I + 1II–9I anaphase I configurations in nearly 8 percent of the PMCs of Coix gigantea (2n = 20) belonging to the tribe Maydeae of the family Poaceae. The behavior of the nondisjoined bivalent during meiosis suggested a much wider range of chromosome number in the gametes (n – 1 to n + 3) than normally believed (n – 1 and n + 1). Isolation of an aneuploid series from nullisomy (2n – 2, 2n = 18) to hexasomy (2n + 4, 2n = 24) also suggested the formation of gametes carrying 9 to 13 chromosomes not only during microsporogenesis but also during megasporogenesis. Higher polysomic constitutions of 2n + 5 and 2n + 6, although possible on theoretical grounds, have not been observed in the population so far since gametes with high chromosome number (n = 13) are rare, and rarer still are the chances of their mating with one of a similar type. The exact mechanism that led to the selective nondisjunction of a bivalent, and always the same bivalent, both in the male and female gametes is not clear. However, nondisjunction in C. gigantea is not accidental but seems to be a regulated event with a definite purpose since better adapted nullisomicsd (2n = 18) that now dominate the population here have been produced by these diploids in a single step.