>>13453920the avg human carries around 2-10 lethal alleles, depending on what you count as lethal and which paper you cite from.
A lethal allele is a genetic variant that if you get the same one from your mother and your father kills you before adulthood; this is why incest is problematic: it leads the offspring (after some generations) to be more likely to inherit the same lethal alleles, or alleles causing genetic diseases.
