Affinity Distance Values among Somatic Metaphase Chromosomes in Maize.
In maize root-tip metaphase preparations, all distances between two chromosomes were measured in 50 cells from each of seven stocks and in 30 from one stock; four were arrested with cold, two with 8-hydroxyquinoline, one with colchicine and one with monobromonaphthalene. Standardized, affinity-distance values were calculated for all pairs of homologues and pairs of nonhomologues from each preparation. The homologues of pair X were the least separated, those of pair I the most separated in the cold-arrested stocks. All but pairs I and VIII were shown to be significantly different from the observed mean. The observed mean was less than but not significantly different from the theoretical value for a random distribution. The use of chemical agents for metaphase arrest increased the separation of homologues, except for pair I.-Eleven percent of the comparisons of nonhomologues from cold-arrested, as contrasted to none of the comparisons from the c-metaphase treatments, were significantly different from the theoretical value for a random distribution. This was considered evidence for limited primary nonhomologue association in maize. Although there were specific, differential responses to the two arrest agents, the population of homologous pairs approached a random distribution only in chemically arrested stocks.-Primary homologue association was considered to be maintained by two mechanisms, the more common involving the microtubules and the second involving the nucleolus.-Interpretations are offered regarding the claims of somatic association in other species, especially man. The opportunity in maize for experimentally modifying distance values by cytogenetic techniques is discussed.
Horn
J D
JD
Department of Plant Sciences, University of Western Ontario, London, Ontario N6A 3K7.
Walden
D B
DB