Summary
Random changes in allele frequency that have strong effects in small populations, including the founder effect and bottleneck.
In depth
Chance events change allele frequencies, especially in small populations; alleles can be fixed or lost with no adaptive reason. The founder effect arises when a few colonists carry a non-representative sample, and bottlenecks reduce populations suddenly.
Drift is a main source of differences among isolated populations.
Drift is stronger the smaller the population: the change in allele frequency per generation scales with 1 over twice the population size. Eventually one allele fixes. A neutral allele takes on average about 4N generations to fix.
The bottleneck effect follows a drastic reduction in numbers such as disease or hunting, and the founder effect arises when a small group establishes a new population: the Amish and Ashkenazi Jewish populations show raised frequencies of some rare disease alleles, and Pingelap Island has a high rate of colour blindness (achromatopsia).
Frequently asked questions
What is Genetic Drift?
Random changes in allele frequency that have strong effects in small populations, including the founder effect and bottleneck.
Which area of biology covers Genetic Drift, and how advanced is it?
Genetic Drift is one of the 54 topics in Genetics. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Population Genetics Models, Allele, Genetic Variation.
Why does Genetic Drift matter?
Drift can fix harmful alleles in small populations and works alongside selection, as in the neutral theory of molecular evolution.
Can you give an example of Genetic Drift?
Ellis-van Creveld syndrome is unusually common in the Old Order Amish due to a founder effect.
What should I learn before Genetic Drift?
Work through the Beginner topics in Genetics first, such as Heredity, Gene, Allele, then return to Genetic Drift. Advanced topics assume the Intermediate vocabulary.
What topics are related to Genetic Drift?
The closest topics to Genetic Drift are Population Genetics Models, Allele, Genetic Variation, Heritability. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Genetic Drift?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Genetic Drift. To practise the whole of Genetics, use the Genetics quiz.
How is Genetic Drift different from Population Genetics Models?
Genetic Drift: Random changes in allele frequency that have strong effects in small populations, including the founder effect and bottleneck. Population Genetics Models: Mathematical models using selection, mutation, drift and migration to predict allele frequency change. Read both side by side and note what each one explains.
How should I study Genetic Drift step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Population Genetics Models and explain the difference aloud. Finally, take the Genetics quiz and come back to this page for any question you miss.