Poisson analysis on the distribution of x-ray induced crossovers in spermatocytes of Drosophila.

Abstract

T o explain the basis of distorted segregation ratios arising in a variety of situations in the Drosophilia male such as the Bar-Stone translocation (Novitslii and Sandler, 1957), heterozygotes for the X.Y and a fragment homologue (Lindsley and Sandler, 1958, heterozygotes for SD (segregation-distorter, Sandler, Hiraizumi, and Sandler, 1959), hnd the non-random behavior of X and Y in sc'-schmales (Gershenson, 1933; Sandler and Braver, 1954; Zimmering, 1963), Peacoclc and Ericlison (1965) have suggested the following hypothesis. They propose as a regular feature of meiosis the existence of a and a pole at the first division, two functional sperm being formed ultimately from the former and two non-functional sperm from the latter. Consequently, segregants included into cells arising froill the pole are recoverable, while those included into cells arising from the pole are not. Thus, distorted segregation ratios are visualized as arising from a non-random movement of segregants to these poles. It should be noted that the original suggestion that not all products of spermatogenesis may be functional was made by Novitslii and Sandler, 1957. Now, a prediction from this model postulatinga and pole, would be that from a meiotic exchange generating reciprocal products which then segregate at the first division, only one of these products is recoverable. This is so because one of the products will proceed to the pole. It would follow, then, that each recovered exchange will have arisen from an independent event. One line of evidence of independence would be that the distribution of crossovers does not deviate significantly from a Poisson distribution. Data bearing on this point are presented below.