 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.