Question

Some mutations result in proteins that function well at one temperature but are nonfunctional at a different (usually higher) temperature. Siamese cats have such a "temperature-sensitive" mutation in a gene encoding an enzyme that makes dark pigment in the fur. The mutation results in the breed's distinctive point markings and lighter body color.

Answer 1

Let's complete the question by adding the missing piece of information

The mutation results in the breed's distinctive point markings (ears, mask, tail and legs) and lighter body color. Use this information to explain the pattern of the cat's fur pigmentation.

Answer:

The mutation of the TYR gene results in the enzyme tyrosinase to be heat susceptible. Tyrosinase takes part in the production of melanin to give darker fur in colder areas. The areas like the tail, legs, ears, and face do lack as much body heat and so will get darker.

Explanation:

A unique protein (enzyme), known as tyrosinase, is the major workhorse in the development of the melanin. A research team from the University of California, USA, led by L. A. Lyons, discovered that Siamese cats have tyrosinase that went through mutation due to the changes in the DNA helix and is temperature-sensitive as it's activity reduces with a rise in temperature. This explains why cat’s warm parts of the body are coated with white, melanin-lacking hair since Tyrosinase is deactivated in these regions and melanin is not developed – hair is white-colored. On the other hand, in cooler boundary the enzyme is active and the melanin is formed – hair has dark color.