|Image was provided by Ashley over at Swamp Dog Blog and is copyright to her.|
The three dogs in this picture are, from left to right: Tahsis, Charlie, and Monkey. They are siblings from the same litter, with a forty pound black Labrador mix mother and an unknown father. In the litter of ten, half was black and half was yellow, and half had short hair while the other half had long hair. Tahsis and Monkey (who are the two yellow females) both have hip dysplasia. Now, what's their genotype?
In truth, there's only a couple of genes that can be guaranteed to be present in these three dogs. For Tahis and Money, they are expressing the recessive red phenotype, which is present in Labrador retrievers and in the breeds that I suspect went into the rest of their ancestry (see below). This would make the two of them ee recessive red. As for Charlie, he is clearly black. He must be dominant black, which is again present in Labs, but also the breeds below as well. I suspect that he is KK black, and that his sisters are likely the same under the recessive yellow. Charlie is also likely to be Ee black carrying recessive red for the reasons I list below. As for their coat length, the long coat seen in Tahsis and Monkey is another recessive trait. Specifically, it is recessive to shorter lengths (though the specific length of "shortness" can vary). So, the girls must be ll long coated, while Charlie is probably Ll short coated carrying long coat.
When it comes to their breed ancestry, I suspect that the mother was likely some sort of mix of Labrador retriever and either golden retriever or spaniel (possibly a Cocker due to her small size). The father was probably a golden retriever. Remember that both recessive red and long hair are recessive to black and short hair, respectively, so that 50/50 proportions of the litter make me suspect that the mother was heterozygous and the father homozygous for the recessive traits. Hip dysplasia is also a recessively inherited (likely polygenic) trait that is quite commonly seen in retreievers. In addition, the three in the image look almost like they're purebred retrievers, so it's most likely that they're mostly of that lineage. Fundamentally, most of the retrievers are quite similar in overall size and body structure