Siamese, burmese and himalayan cats all have temperature sensitive mutations in the C gene. These mutations are all recessive and the different alleles are indicated with superscripts. A cc genotype would give an albino cat, but these are rare. Temperature sensitive mutations exist however, such that the C gene, which is required for production of any pigment, is only active at low temperatures. What this means is that on the parts of the cat where the temperature of the hair follicles is high, the C gene is inactive or less active, resulting in less pigment. However, on the points (ears, nose, feet and tail), the temperature is slightly cooler, and the C gene is active and pigmentation is darker. The difference between siamese, burmese and balinese, is the degree to which the pigmentation is shut off at the normal body temperature. Himalayans have the siamese allele, but long hair. Other features of these breeds are different, but not covered in our class exercise, such as body and head shape, eye color, etc. Here are some pictures to illustrate these cats.

It is unusual to see piebald spotting in these cats. However, due to the light color of some, it would be hard to detect if it were there. Look at the points to see if there are any patches of white, rather than the gradient of color from the extremities to the body.

This is a seal point siamese. If not for the cscs genotype, it would be a black cat
The genotype is L_ aa oo D_ ww ss cscs.

These are burmese. The C gene is the burmese allele, cbcb. It is less temperature sensitive than the siamese allele so the warm parts of the body are darker. These would also be black cats without the burmese allele.
The genotype is L_ aa oo D_ ww ss cbcb.

Himalayans are basically long-haired siamese, with respect to coat color. There are other differences, but not with any of the genes we are scoring. With himalayans, the long hair will make the cat warmer, so the tail especially will be lighter in color than in siamese.
The genotype is ll aa oo D_ ww ss cscs.

The purebreds include:

seal point - aa oo D_ ww ss cscs

chocolate points are the same as seal points except that they have a mutation in the B gene (they are bb) that makes the black pigment a chocolate brown instead. We are not scoring the B gene in this study because it is very rare in this area except in purebreds - aa oo D_ ww ss bb cscs

blue point - aa oo dd ww ss cscs

lilac point - aa oo dd ww ss bb cscs

red (or flame) point - aa OO D_ ww ss cscs (or OY if male)

More information on cat breeds: http://www.fanciers.com/breeds.html