Maternal effect dominant embryonic arrest

Maternal effect dominant embryonic arrest (Medea) is a selfish gene composed of a toxin and an antidote. A mother carrying "Medea" will express the toxin in her germline, killing her progeny. If the children also carry "Medea", they produce copies of the antidote, saving their lives. Therefore, if a mother has one "Medea" allele and one non-Medea allele, half of her children will inherit "Medea" and survive while the other half will inherit the non-Medea allele and die (unless they receive "Medea" from their father).
Medea's selfish behavior gives it a selective advantage over normal genes. If introduced into a population at sufficiently high levels, the "Medea" gene will spread, replacing entire populations of normal beetles with beetles carrying "Medea". Because of this, "Medea" has been proposed as a way of genetically modifying insect populations. By linking the "Medea" construct to a gene of interest - for instance, a gene conferring resistance to malaria - "Medea"'s unique dynamics could be exploited to drive both genes into a population. These findings have dramatic implications for the control of insect-borne diseases such as malaria and dengue fever.
Construction of Medea.
Medea, which has been found in nature only in flour beetles, is the only selfish gene that has been simulated in the lab and tested in the fruit fly "Drosophila melanogaster". The toxin was a microRNA that blocked the expression of "myd88", a gene vital for embryonic development in insects. The antidote was an extra copy of "myd88". The offspring receiving the extra copy of "myd88" survived and hatched, while those without the extra copy died. In lab trials where 25% of the original members were homozygous for "Medea", the gene spread to the entire population within 10 to 12 generations.
Etymology.
Medea was named for the Greek mythological figure of Medea, who killed her children when her husband left her for another woman.