

A conditional mutation is a mutation that has wild-type (or less severe) phenotype under certain “permissive” environmental conditions and a mutant phenotype under certain “restrictive” conditions. For example, there is an enzyme that catalyzes the production of the pigment responsible for dark fur color in Siamese cats and Himalayan rabbits. The enzyme is heat sensitive, meaning that it does not function at higher temperatures. Rabbits raised at 5°C are all black. If raised at 20°C, they are white with black paws, ears, and noses. When raised at 35°C, they are all white. Similarly, a snowshoe hare exhibits seasonal fur coloration. Hares living in 5°C are all white to provide camouflage in the snow; hares living at 35°C have brown fur to provide camouflage in their forest habitat. 2. For the Siamese cat and the Himalayan rabbit, which of the following best represents an activity curve for this enzyme: a or b? Explain why you think so. a. Supposing that the snowshoe rabbit had a conditional mutation resulting in seasonal fur coloration, which of the following curves could represents an activity curve for this enzyme: a or b? Explain why you think so. (Please note, this is not how it really works for snowshoe rabbits. The coloration ina snowshoe hare is due to molting, based on day length rather than temperature. You do not need to fit that into the question. I am forcing the snowshoe hare example to fit here.) b. Fast Fast Slow Slow 5 10 15 20 25 30 35 40 45 50 5 10 15 20 25 30 35 40 45 50 Temperature (°C) Temperature (°C) a. b.





