Chromosome-exchange Sites inTradescantia PaludosaMicrospores

Abstract

The distribution of chromosome-exchange aberrations between cells, induced by radiation in Tradescantia paludosa micro-spores 4 days before pollen-grain mitosis, has been investigated. Gamma-, X-and neutron-radiations given at a variety of dose-rates, and under different environmental gas conditions, are represented in the data. Dicentric plus centric ring types conform to a binomial distribution (p+q)n with n=2-4, over the whole yield range investigated. If n is equivalent to the average number of "sites" available for exchange, this is strong evidence that these are pre-determined physical entities. When dicentric and centric rings are considered separately, each type conforms to a binomial with n=2-0. Non-additivity of the n values suggests that differences in probability exist at the 2 types of site, and a spurious n value arises from pooling. Some possible reasons for this difference between sites are considered.