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 breeds distinctive point markings and lighter body color (see the photo). Using this information and what you learned in the chapter, explain the pattern of the cat's fur pigmentation. For selected answers, see Appendix A.

Answer 1

In case of Siamese cats, we can see temperature sensitive mutation, the cats will have dark ear tips, nose and feet and this is because of temperature sensitive mutation in the c locus. This c locus is responsible for fur color. But the same protein will not be functional at higher temperature.

Wild type alleles C is dominant and when it is expressed it causes full pigmentation.

c^s allele is recessive and cats will have characteristic distribution of dark color like you can find it on ears, tails and legs in its homozygous condition (c^sc^s). At low temperature, the tyrosinase enzyme encoded by c^s is active and thus it will lead to the production of melanin. But at high temperature the activity of tyrosinase will get affected and the cats will be in their light color.