Induction of chromosome doubling at meiosis by the elongate gene in maize.

EIOSIS is a highly integrated system characterized by the orderly procession of events such as pairing, recombination, chiasma formation, and disjunction, which culminates in a reduction o€ chromosome number in the gametes. That this system is under genic control has long been evident from the many mutant genes reported in plants and animals which affect specific stages of the meiotic system. These meiotic genes are of unusual interest in that a thorough study of the physicochemical basis of their action gives promise of leading to a better understanding of the physiological conditions which bring about the transsition from mitosis to meiosis as well as of the cellular environment essential for such critical events as synapsis, recombination, and disjunction. A discussion of the genetic control of meiosis is given in REES (1 961 ) . A new meiotic gene is reported in this paper which will be a useful tool in cytogenetical studies with maize. This mutant was found in the open-pollinated variety Hays Golden. It is a simple recessive and has not yet been placed in a linkage group. This new meiotic gene is called elongate (el) because of the elongated appearance or despiralization of the chromosomes at both meiotic anaphases, but it has a number of other effects. The most significant of these is the production of unreduced eggs which occur in varying proportions with haploid eggs. Evidence will be presented that the diploid eggs originate by chromosome doubling at the second meiotic division. The recovery of two of the four chromatids of a bivalent in the diploid eggs of elongate plants enabled a half-tetrad analysis and data were obtained which bear on the questions of chromatid interference and centromere mapping.