Figure 2. Parental Crosses Representing the Reproductive Advantage of the Medea Allele.

Females carrying the Medea allele produce a maternally expressed toxin (red outer circle) that is deleterious to their offspring. Offspring who carry the Medea allele are rescued by a zygotically expressed antidote (green inner circle) expressed by the same allele. Offspring of heterozygous females who do not inherit the Medea allele are killed by the toxin because they lack the antidote (yellow represents lack of the toxin/antidote). This distorts the offspring ratio in favor of the Medea allele.