Founder Effect

“A new island may receive a tiny, unrepresentative sample from the mainland.”

01 / PLAINLY

What it means, plainly

The founder effect occurs when a few colonists establish a population carrying only part of the original variation.

02 / CONTEXT

A little more

Founders carry a sample of alleles whose distribution can differ by chance from the source population. The new population may have lower diversity and unusual frequencies even without selection during travel.

03 / WHY IT MATTERS

Why it matters

It explains initial differences after colonization and highlights genetic risks in small, isolated populations.

04 / EXAMPLE

A familiar example

Five seeds carried by birds may found an island population where a color rare on the mainland becomes common.

05 / LIMIT

What it does not mean

Not every colonist difference proves a founder effect; selection and later migration can also matter.

06 / NOTICE

Notice it in your day

Draw five pieces from a bag of several colors and use them to fill another bag. Repeat and compare populations.

FINAL NOTE

The idea worth keeping

Compare initial size, diversity, and frequencies with the source, separating chance from later adaptation.

QUESTIONS / 02

Questions people still have

Is it the same as a bottleneck?

Both involve small samples, but a founder event starts a new population while a bottleneck shrinks an existing one.

Does diversity recover as numbers grow?

Population size can rise quickly, but restoring lost variants requires mutation or gene flow and usually takes longer.