Coat colour genetics

Labrador Retrievers come in three distinct colours: black, yellow and chocolate. The colour of a dog depends on the presence of pigments in skin and hair. The pigments occur as two distinct types. The first type is essentially yellow. The second one is dark, and varies from black to brown. The type of pigment that a Labrador produces depends on its genetic make-up and is the result of an interaction between two different genes, which are called the E and the B gene.

A dog's genome consists of two sets of genes, one from each of the parents. So for each gene, if different forms exist, a dog can have two forms of the gene.

Different forms of the E and the B gene exist. The difference in the genes is distinguished by uppercase and lowercase letters. So the E gene exists as E and e, while the B gene exists as B and b. Therefore, depending on the parents, a dog genome may be EEBB, EeBb, eeBb or any other combination.

The form that is written in an uppercase letter is called the dominant form. This means that, if a dog has both forms of a particular gene, it is the form that is written in capitals that has an effect on the dog — it is expressed. If there is no dominant gene the recessive (lower case) one will be expressed. For example, for a dog with eeBb, the e and the B forms will be expressed.

Black dogs can have 4 possible genomes
- BBEE : pure (dominant) black
- BbEE : black carries chocolate
- BBEe : black carries yellow
- BbEe : black carries yellow and chocolate

Yellow dogs can have 3 possible genomes

- BBee : yellow carries black

- bbee : yellow carries chocolate

- Bbee : yellow carries black and chocolate

Chocolate dogs can have just 2 possible genomes

- bbEE : pure chocolate

- bbEe : chocolate carries yellow

A great chart showing the possible combinations and outcomes can be found here

http://www.vetdnacenter.com/files/coat-color-predictor.pdf

Of course these just show the probability of the outcome. I don't know which type Jess is (bbEE or bbEe) must most chocolate dogs are bbEE as matings between yellow and chocolate is not common (partly in reason as it can produce yellow pups liver noses). Regardless of Jess' genome, Reed is a black carrying chocolate (BbEE) so the probable outcome is the same (as can be seen from the chart above) : 50% chocolate pups and 50% black pups. Of course you may get 100% black or 100% chocolate but somewhere in between is a more likely outcome.

In case this has only just whet you're appetite :) a far more detailed look at colour coat genetics can be found here

http://www.labbies.com/genetics2.htm