## Genetic drift: effective population size

We began our study of genetic drift last Thursday and learned several important things:

- There will always be some amount of randomness to the change in genotypic composition between generations simply because the offspring represent a sample from the parental generation.
- The larger the population size, the larger the sample and the more similar the offspring population is likely to be to the parental population.
- The impact of genetic drift is smaller in large populations than it is in small ones.
- Any finite population will lose genetic diversity over time unless mutation or migration introduces new genetic variants.
- Small populations will lose diversity more rapidly than large ones.

I hope you remember that the mathematical properties of genetic drift depend on additional assumptions, e.g., no separate sexes, constant population size. Today we'll dive into the concept of “effective population size” and explore how to understand the properties of genetic drift in real populations that violate those assumptions.