Testing the Dominance Theory

Figure WN22.6. The dominance theory can be tested by constructing “unbalanced” females, which carry two X chromosomes from the same species. If F₁ males are inviable because they carry a recessive allele that is incompatible with the hybrid autosomal genotype (top), then F₁ females with heterozygous X chromosomes will be viable (middle). However, the recessive allele will be expressed in “unbalanced” females that have homozygous X chromosomes, just as in the F₁ male (bottom). (After Fig. 2 of Orr 1997a.)