Multiple Allele Traits (Epistasis) in Labrador Retrievers
In labradors, coat color is controlled by two sets of alleles. Black is dominant to brown, but yellow is epistatic, when two yellow alleles are present (ee), the yellow coat color is expressed, independent of the brown/black alleles present.
The dash (missing allele) indicates that the allele may be dominant or recessive. It will not affect the phenotype.
1. On the cross pictured, what must be the genotypes of the two parents for the outcome to produce at least one yellow labrador puppy but NO chocolate puppies.
____________ x _____________
2. Show the following cross and describe the phenotypic ratios. A punnett square or a mathematical ratio can be used to solve this.
BbEe x BbEe
3. Show the following cross and describe the phenotypic ratios.
BbEe x bbee
4. Show the following cross and describe the phenotypic ratios.
bbEe x bbee
5. If a chocolate lab carries a yellow allele, what would be the ratio of the offspring if it is bred with a yellow lab that is heterzygous for the black/brown coat color gene. (Hint: Work out the genotypes of parents first!)
Other Resources on Genetics
How to Solve Dihybrid Crosses – step by step guide on setting up 4×4 squares and determining ratios
Advanced Bunny Genetic Crosses with two traits – also includes fruit fly genetics
Explore the Genetics of Corn Snakes - 2 sets of genes determine snake colors
Multiple Allele Traits in Chickens – shows how combs are inherited (rrpp x RRpp)
Credit: Images of labradors were taken from a variety of creative commons photos, sources summarized below: