X Chromosome Inversions and Meiosis in Drosophila Melanogaster

Abstract

It has been shown above that crossovers between X chromosome segments inverted with respect to one another influence the orientation of the meiotic tetrads in such a way as to eliminate the single crossover chromatids, leaving a normal non-crossover one in the reduced egg nucleus. The more complex results expected from multiple exchange are analyzed and shown to give results in agreement with observation. It seems probable that the scheme outlined in this paper will apply for the case of inversions that do not include the locus of the spindle attachment and for other chromosome aberrations in which crossing-over gives rise to chromatids with two spindle attachments, and where the conditions of meiosis are such that (a) the meiotic spindles are oriented so that the reduced nuclei lie approximately on a single straight line, and (b) only one of the terminal nuclei functions in further development. These conditions obtain in megasporogenesis in most seed plants, as well as in oögenesis in most animals.