Relationship between chromosome content and nuclear diameter in early spermatids of Drosophila melanogaster.

We have studied, using light microscopy, the relationship between chromosome content and nuclear diameter in early spermatids of males carrying different combinations of wild-type and compound chromosomes in Drosophila melanogaster. By using these genotypes we have been able to observe spermatid nuclei bearing various numbers of chromosomes ranging from only one sex chromosome and no major autosomes to almost twice the normal chromosome complement. We have found that variations in the chromosome content are accompanied by increasing the variance in early spermatid nuclear diameter; the more gametic classes produced, the higher the variance of nuclear diameters. These results indicate that measuring nuclear diameters in early spermatids represents a useful way to estimate the levels of meiotic non-disjunction and thereby to improve the characterization of lethal or male sterile mutants in which analysis of meiotic chromosome non-disjunction cannot be achieved by conventional genetic methods.