Explain how genetic drift can affect allele frequencies in a small isolated population. Consider a population of 10 diploid individuals where allele $A$ has an initial frequency of $0.5$. What is the probability that allele $A$ will eventually become fixed?

Step-by-step solution

1. Define genetic drift as random sampling of alleles each generation.
2. State that in a population of size $N$ alleles are sampled binomially, leading to random changes in frequency.
3. Explain that over many generations a neutral allele can eventually be fixed or lost purely by chance.
4. State the general result: for a neutral allele the probability of eventual fixation equals its initial frequency.
5. Apply to the given example: initial frequency $p=0.5$, so the probability that $A$ becomes fixed is $0.5$. (If one wants the probability that fixation occurs in exactly one generation, calculate $p^{2N}=0.5^{20}\approx 9.77\times 10^{-4}$, but this is not the long‑term fixation probability.)

Concept tested: Genetic drift and fixation probability

Published 19 September 2026 · How this solution was prepared and checked