How is the probability that a particular allele is eventually fixed by genetic drift determined?

The probability that a particular allele is eventually fixed by genetic drift is primarily determined by the allele frequency in the population. When considering genetic drift, which is the random change in allele frequencies over time, the initial frequency of the allele plays a significant role. If an allele is common, it has a higher likelihood of being fixed compared to a rare allele, simply because there are more copies contributing to the gene pool.

In small populations, genetic drift can cause significant fluctuations in allele frequencies, making it possible for alleles present at low frequencies to become fixed purely by chance. Conversely, in larger populations, although there may be greater stability in allele frequencies overall, even a moderate frequency of an allele can lead to its eventual fixation.

The other factors mentioned, such as population size, environmental factors, and mutation rate, do influence genetic drift and allele fixation indirectly, but the immediate and direct factor determining the probability of fixation is the allele frequency itself.