One of the best examples of “gene-environment interaction” is the gene (allele) producing the coloration of Siamese cats. The expression of this gene depends heavily on the ambient temperature that the skin experiences while the fur is growing. Cat World describes it (read this web page for a lot more information, particularly if you have a Siamese or Himalayan):
Siamese cats carry a gene known as the Himalayan gene. This gene is seen in other species, such as the rabbit and the mouse. It is a mutation at the C locus and it causes partial albinism. This gene is recessive to the full colour C gene. This means you need two doses of it (homozygous) for the Siamese colour to show up. If you mate a Siamese to a Siamese, you will get Siamese offspring. If you mate a Siamese to a black cat, you will get black offspring which will carry one dose of the Siamese (cs) gene at the C locus.
The Burmese also shares the same type of gene, which is known as cb.
The cs and cb genes are co-dominant and hence if you mate a Siamese (cs) to a Burmese (cb) you will get a Tonkinese (cs/cb), which has “mink” colouring.
This gene is heat sensitive, the cooler the area, the darker the colour. Which explains why a Siamese has dark extremities such as the face, tail and legs. The body being the warmest part of the cat remains lighter in colour. You will notice your Siamese get darker in the winter months, especially if your Siamese is an indoor/outdoor cat. Siamese cats are white at birth, this is due to being in the constant warmth of the mothers womb. This colouring varies from Siamese to Siamese.
Courtesy of my friend the British geneticist Steve Jones, here are three pictures of Siamese cats that experienced different temperatures:
First, a “normal” Siamese:
Next, Siamese living in a cold environment. Note the heavy dark pigmentation appears more widely over the body:
This is a Siamese living in a hotter climate. It’s almost white, and note the tabby-like pattern that now appears on the tail:
Finally, someone has shaved his initial into the side of this cat, which then re-grew the fur under cold conditions.