In Labrador retriever breed of dogs, coat colour is determined by several genes.

Question

In Labrador retriever breed of dogs, coat colour is determined by several genes. One gene determines the black or chocolate coat colour, with the black colour (B) dominant over chocolate (b). Your neighbour owns two Labradors from the same litter, both female, one black, one chocolate and he paid 5000 dollars to send his black Labrador female to breed with a champion black Labrador owned by a disreputable character. He 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 explanation for this? thank you.

Explanation / Answer

The coat color of the Labrador Retriever is controlled by two different genes. One gene controls the coat color and the other gene regulates the gene and the amount of gene pigment deposited. An offspring with one or two B's has a black nose while one with two b's has a brown nose. So this means if either gene from a parent is B the offspring will be of black coat color. The genetic combinations will include:

BB= both the parents provide black color gene

Bb= mother supplies back nd father supplies chocolate or vice versa

bb= both the parents provide a chocolate gene

An offspring with a B gene will have black nose while one with two b's will have a chocolate nose. Along with this the second gene E and e influence the coat color. The little 'eee' genes are able to influence the color and are able to switch off the 'bee' gene that causes the black and chocolate coat colors. Each dog inherits two 'eee' gene, one from each parent. The dominant E and it does not interferes with the 'bee' gene while the little e has the potential to mask off the effect and switch off the 'bee' gene that will give black or chocolate dog. The result of this effect is a yellow dog.

Here the mating is between a black dog and chocolate dog. The possibility is that the black labrador is with EEBb genotype while the chocolate labrador is with Eebb genotype. So when mated, EEbb and Eebb genotypes are produced. Due to which the 7 puppies are chocolate out of 12.

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