What condition allows the expression of the Himalayan allele in rabbits?

The expression of the Himalayan allele in rabbits is a classic example of a temperature-sensitive pigment mutation. This allele is characterized by the presence of a coat color pattern that varies based on the temperature of the rabbit's body. The mutant allele causes the production of dark pigmentation only at cooler body temperatures.

In low-temperature environments, such as the extremities of the rabbit (ears, paws, and tail), dark pigments are produced, resulting in a black or dark brown coloration in those areas. However, when the temperature rises, particularly in warmer areas of the body, the production of pigment decreases, leading to a lighter beige or white coloration in the body fur.

Thus, low temperatures promote the expression of the Himalayan trait, making this condition the correct answer, as it directly influences the gene's expression due to temperature sensitivity.