Effect of the environment on coat color in the Himalayan rabbit Animation

An organism's phenotype—the combination of traits that we observe—is the product of interactions between its genotype and the environment. For example. a Himalayan rabbit is completely white at birth. But within weeks, the fur on the rabbits ears, nose, tail. and lower legs darkens. The rabbit is homozygous for an allele that encodes a heat-sensitive enzyme. The enzyme catalyzes a step in the synthesis of the brown pigment melanin. In central body regions, metabolic heat disables the enzyme. no melanin is produced, and the fur remains white. In cooler body parts. the enzyme is functional. melanin is produced. and the fur is tinted brown. The effect of temperature on the rabbit's phenotype can be demonstrated by shaving a patch of fur, and keeping the area cool as it grows back. In the artificially cooled area, the heat-sensitive enzyme remains functional, melanin is produced, and the fur grows back dark.

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