## Fst and genetic drift in small populations

Key to genotype colors:

- AA (yellow)
- Aa (orange)
- aa (red)

The frequency of allele **A** used at the start is *p* = 0.5 for all populations. Refresh your browser to start over.
Scroll down for more details.

## Details

The following keys do something:

- ‘n’ advances to the next generation
- ’s’ toggles between 4 and 16 diploid individuals per population
- ‘h’ hides population boundaries

The status text shows:

**g**= the number of generations of random mating within populations**pmean**= mean frequency of the A allele (*p*) over all populations**Ho**= observed heterozygosity = fraction of heterozygotes over all populations**He**= expected heterozygosity = expected fraction of heterozygotes = 2 pmean (1-pmean)**Fst**= variance of*p*across populations divided by pmean (1 - pmean), which is the maximum possible variance of*p*across populations

The **blue histogram** at the top shows the distribution of *p* over the 12 populations (*p* = 0 at far left, *p* = 1 at far right).

With each new generation, drift increases the variance of *p* across populations and thus
increases **Fst** (indicated by the fraction of the status bar filled with **orange**) until, eventually,
all populations are fixed for either the **A** or the **a** allele, the variance of *p* is
as large as it can get, and **Fst** equals 1.

## Acknowledgements

This applet makes use of the excellent d3js javascript library. Please see the GitHub site for details about licensing of other libraries that may have been used in the source code for this applet.

## Licence

Creative Commons Attribution 4.0 International. License (CC BY 4.0). To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.