Labrador Retrievers have been bred for quite a while and the yellow color of som

Question

Labrador Retrievers have been bred for quite a while and the yellow color of some Labradors can come with either a brown (chocolate or liver) colored nose or a black nose. While black and brown eumelanin are determined as in cats by the B locus, Labradors are also all KK. The K locus determines whether the dog is solid in color or has some type of black and tan coloring. There is also an extension locus E that has 5 known alleles that affect coloring. In purebred Labradors only the E allele, which allows for a full color dog, and the e allele, which stops eumelanin from being made in the coat, are present. This makes four possibilities in Labrador Retrievers: Black coat/Black nose(B-E-) Brown coat/Brown nose(bbE-) Yellow coat, Black nose(B-ee) Yellow coat/Brown nose(bbee) 1. (2 pts) If you breed a black lab to a bbee yellow lab and get 25% yellow puppies with brown noses, what was the black lab's genotype?

Explanation / Answer

Black lab black nose genotype is.........BbEe.....gametes are BE, Be,bE,be yellow lab brown nose genotype is........bbee.........gametes are be When black lab has genotype BbEe, yellow lab has genotype bbee, each phenotype appears at a raio of 25%. BbEe (black coat black nose).........25% Bbee (yellow coat black nose)...............25% bbEe (brown coat brown nose)................25% bbee (yellow coat brown nose) ...............25% BE Be bE be be BbEe (black coat black nose) Bbee (yellow coat black nose) bbEe (brown coat brown nose) bbee (yellow coat brown nose) BbEe (black coat black nose) and chocolate lab bbEE gives............ BbEe.....gametes are BE, Be,bE,be bbEE....gametes are bE During this cross, yellow phenotype can not be observed. BE Be bE be bE BbEE (black coat chocolate nose) BbEe (black lab black nose) bbEE (brown coat chocolate nose) bbEe (brown coat brown nose) BbEe (black coat black nose) and chocolate lab bbEe gives............ BbEe.....gametes are BE, Be,bE,be bbEe....gametes are bE, be During this cross, yellow phenotype can be observed. The phenotype ratio is: 2:1:1:1:2:1 out of 8 , two are with yellow coat and 3 are with brown noses. BE Be bE be bE BbEE (black coat chocolate nose) BbEe (black coat black nose) bbEE (brown coat chocolate nose) bbEe (brown coat brown nose) be BbEE (black coat chocolate nose) Bbee (yellow coat black nose) bbEe (brown coat brown nose) bbee (yellow coat brown nose)

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