A rare allele has a frequency of 5 per cent in a large source population…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A rare allele has a frequency of 5 per cent in a large source population. Five individuals leave the source and start a population on an island. Each has two copies of the gene, picked at random from the source population.
- What is the chance that none of the ten gene copies is the rare allele?
- How many copies of the rare allele are expected among the founders?
- If exactly one copy is present among the founders, what is the allele frequency in the new population at the start?
Need a reminder? The key ideaShow
Gene flow: . A founder group of individuals has gene copies, and a rare allele is missing with the chance . Drift in a small population is strong, and it wears away the heterozygosity by a factor in each generation.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. and founders, so gene copies.
Plan. Use the chance of no hit in independent tries.
Step 1. (a) , which is per cent.
Step 2. (b) copies.
Step 3. (c) One copy in is .
Answer: per cent; copies; .
Check. In about six of ten such colonies the rare allele is missing, and in the others it is at least twice as common as in the source. The founder effect can go either way.
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