Answer:
The correct answer is 1. Greater than 0%. An allele to become common must have a frequency of at least 0.005%
Explanation:
A polymorphic gene has more than two alleles. The more alleles there are in a population, the more polymorphic the gene is.
In a polymorphic gene, the allelic frequency of the most common allele must be minor of 99%, while the less common allele must have an allelic frequency superior to 0.005%. If any allele does not reach this frequency in the population, it is not considered to be common. In fact, it is considered to be a rare allele.
