Figure 8. Karyotypic relationships of the clarkii group species. A. The standard karyotype (S. mucronatus, ♀ F6300), B. the clarkii karyotype ♀ (F5101), C. the melanorhinus karyotype, heterozygous for the Em mutation ♂ (Y44250), D. the asper karyotype ♂ (F5809). The chromosomes involved in the X₁X₂Y sex trivalent of melanorhinus are indicated by a black border. The arrows indicate the probable origins of these chromosomes from an ancestral karyotype like that of clarkii. The Em chromosomes of melanorhinus and asper are also indicated by a black border. The bar in the center of the figure represents 10 microns.