A peculiarity of gene frequency estimation

Black wool is due to a recessive gene, the dominant white trait being caused by a duplication, with one or more repeats. The total number of repeats in the diploid genotype can be detected, but a 1/1 and a 2/0 repeat cannot be distinguished. This complicates gene frequency estimation, and in the absence of black sheep, it is shown that very similar data on repeat numbers can give drastically different gene frequency estimates. The (possible) presence of black sheep can resolve the problem.