Return to MCAT® Blog Homepage

MCAT Biology Question — Genetic Drift

Which of the following is (are) true regarding genetic drift?

I. Genetic drift has more pronounced effect on alleles with a low allele frequency than on alleles with a high allele frequency, regardless of population size.
II. Genetic drift is due to random sampling during reproduction.
III. The more isolated a population is, the less pronounced the effect of genetic drift is.


A. I only

B. II only

C. I and II only

D. II and III only

Click for Explanation

When a population reproduces, the alleles in the offspring are a random sample of the alleles in the parental generation. Due to this, changes may occur in the genetic composition of a population due to chance. These changes are genetic drift. Thus (II) is correct, eliminating choice (A).

Genetic drift is less pronounced in large populations that are connected with other populations. When a population is isolated, there is a higher likelihood that a particular allele can disappear entirely, or become entirely fixed. Thus, (III) is false, eliminating choice (D).

Finally, the effect of genetic drift is larger when an allele is less common. The fewer copies of an allele there are, the more likely it is that the allele may disappear entirely due to genetic drift. While genetic drift has a bigger impact on smaller populations, within any given population (regardless of size), the effects of genetic drift will be strongest on alleles with a low allele frequency. Thus (I) is correct and choice (C) is the right answer.

Want more MCAT practice?

We’ve got options for every schedule and learning style!

From the best online MCAT course created by top instructors with 524+ MCAT scores to the most representative full-length practice exams and private tutoring, we can custom tailor your MCAT prep to your goals!

Not sure which option is right for you? Schedule a free MCAT consultation with an MCAT expert using the form below. No obligation, just expert advice.

Create your Free Account to access our MCAT Flashcards SIGN UP NOW
MCAT is a registered trademark of the Association of American Medical Colleges (AAMC), which is not affiliated with Blueprint.