In a particular species, brown fur is dominant over white fur. So how could an individual have tan fur?

In a species where brown fur is dominant over white fur, the presence of tan fur, which is not one of the ordinarily expected phenotypes, suggests the involvement of additional genetic mechanisms beyond simple dominance.

One possible explanation for the existence of tan fur when considering only brown and white fur color options is incomplete dominance. In incomplete dominance, neither allele is completely dominant over the other, and the heterozygote has a phenotype that is intermediate between the two homozygous phenotypes. If we consider the allele for brown fur (B) and the allele for white fur (b), in a case of incomplete dominance, a heterozygote with genotype Bb might have tan fur, an intermediate phenotype between brown (BB) and white (bb).

Another possibility is codominance, where both alleles in the heterozygous state are fully expressed, resulting in a distinct phenotype that includes both parental traits. However, codominance typically doesn't result in intermediate phenotypes like tan but rather a mosaic of both traits (such as spotted or speckled fur).

A third possibility is that an entirely different gene is involved in the production of tan fur. Fur color could be polygenic, meaning that multiple genes contribute to the phenotype. In this case, an additional gene could be influencing the expression of fur color, leading to tan fur in some individuals.

Without more information about the genetic mechanisms at play in this species, we cannot provide a definitive explanation for tan fur. However, the scenarios outlined above are potential genetic explanations for how tan fur could appear in an organism where only brown and white fur colors are expected based on simple dominant-recessive inheritance.