Meiosis VIII: Segregation matrix methods applied to meiotic drive in Drosophila melanogaster males with an SC 4-SC 8 inverted X

Two alternative matrix solutions of drive in Drosophila males with sc⁴-sc⁸ as studied by Peacock (1965) poses questions concerning meiosis in such flies. The two solutions are based primarily on the observations that sc⁴-sc⁸ males with low levels of X, Y non-disjunction produce twice as many female-as male offspring; that 50% of the sperm in this Drosophila line may be dysfunctional; that at all levels of non-disjunction studied, the difference between the % of female and male offspring produced by normal disjunction is about 33; and finally that, among non-disjunction types, nullo sperm werer covered more frequently than those with X and Y.The first matrix solution suggests a new model involving production of one infertile- and one fertile daughter cell at meiosis 1 in 1/3 of the cases and at meiosis 2 in the other 2/3. The second solution is already well known and would require the production of one fertile and one infertile secondary cyte at meiosis 1, in all cases. The unique feature of the first solution is that all four anaphase 2 poles (or genes) are present in primary spermatocytes as primordia. Two of these would predetermine fertility and two, infertility; and by assuming a random 2-by-2 assortment of these four poles at M1, together with physical binding of one of them with an X-or a Y chromatid, all known sc⁴-sc⁸ data as listed above, can be explained. The second model is necessarily more cumbersome, as it is difficult to account for a 2/1, female/male, ratio being produced at one cell division (meiosis 1).Discussed are possible applications of the segregation matrix method as a tool for determining degrees of freedom (complexity) in any biological system; implication of the models for segregation distorter (SD), for heterozygous translocations analyzed in Drosophila by Glass (1935) and by Zimmering (1955), and in other known or suspected cases of drive.