Answer:
C. Only one allele appears for that gene in that population.
Step-by-step explanation:
This totally explains what happens during gene fixation because when it happens in a small population, it tends to make one of its allele to appear for the said gene.
Furthermore, fixation can be explained as the change in a gene pool from a situation where there exists at least two variants of a particular allele to a situation where only one of the alleles is left. In the absence of mutation, any allele must eventually be fixed or lost completely from the population. Whether a gene will ultimately be lost or fixed is dependent on selection coefficients and chance fluctuations in allelic proportions.