A dwindling population of 1000 frogs occupies an isolated watershed in Costa Ric

Question

A dwindling population of 1000 frogs occupies an isolated watershed in Costa Rica. To help preserve the species, scientists caught 20 frogs to start a new population in a nearby watershed. This species has a gene that affects eye shape. The 1000-member wild population has two alleles for this gene: R and r, with frequencies 0.7 and 0.3, respectively. What will be the allele frequencies of R and r in the 20-member founder population?

Imagine a population evolving by genetic drift in which the frequency of allele K is 0.65. What is the probability that at some point in the future allele K will drift to a frequency of 1?

Explanation / Answer

There's absolutely no way to know. That's the point of the founder population. Because the new population is so small, we cannot be certain that the original allele frequencies will be maintained.

If you flip a coin a thousand times, you should get very close to 500 heads and 500 tails. But if you only flip it four times, you could get anything. Similarly, depending on which frogs the researchers happen to grab, the new population could have any mix of alleles. What if they happened to grab only RR frogs? Or all Rr? The new frequency could be very different from the old. That's exactly why we're interested in founder populations as a concept.

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