Question

In Labrador retrievers, a gene (B) determines the black or chocolate coat colour. The black colour (B) is dominant over chocolate (b). Your neighbour owns two Labradors from the same litter, both female, one black, one chocolate. He paid $10,000 to send his black Labrador female to breed with a champion black Labrador. This “champion” is owned by a dishonest character. Your neighbour is not a witness to the mating. Last weekend the neighbour’s dog gave birth to 12 puppies, 7 of which are chocolate colour. What are the most likely and the second most likely explanations for this?

Answer 1

The two females which the the neighbour bought was one black and other chocolate colour. The chocolate colour has the genotype bb (homozygous recessive) and the other black female was obviously Bb (heterozygous) as it gives birth to chocolate puppies.

Out 12 puppies, 7 were chocolate coloured. so ratio is almost 1:1. So the most likely explanation is ,the owner of the champion mated the black female (Bb) with a chocolate coloured male (bb).

P --- Bb X bb

F1------ Bb (Heterozygous black) and bb (Homozygous chocolate) Ratio 1:1