Two populations that don't mix is an example of what's know as the Wahlund effect.
S. Wahlund. Hereditas, 11:65-106, 1928
"Formal genetics" should be as outmoded as the myth that the world is supported on the backs of whales and tortoises.
Lissenko (Regarding the scientific misconduct of Lissenko, a Manichaeist point is the truth)
Cartoons on genetics are intended to teach us that not everything in nature has a function, and this requires a stretch of the imagination.
A mermaid who was heterozygous for hair color (= Gg, green) and who had normal fingers (= ff, mermaids with recessive traits must be homozygous for the recessive allele) had a father with blue hair (= gg) and webbed fingers (= Ff, since daughter is homozygous for the recessive normal fingers allele f) and a mother with green hair (= Gg or GG) and webbed fingers (= Ff).