this question is on genetic drift in biology alevel aqa.
why does genetic drift affect smaller populations more than large ones?
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- Thread Starter
- 12-03-2018 21:51
- 13-03-2018 17:32
- 17-03-2018 12:42
It might make more sense if you think about an example such as a captive breeding program. In my breeding program, I have 20 adults who can reproduce- at the moment let's pretend every animal is Bb for coat colour- so there's an even mix of each allele.
You'd normally expect 25% of offspring to be BB, 50% to be Bb and 25% to be bb- but in a small population things might not perfectly follow this pattern, so say in the next generation, 20% are BB 40% are Bb and 40% are bb.
This is much more likely to happen in a small population where, say, only 10 offspring are born each year than in the large wild population where 100 offspring are born each year- in a large population random chance is more likely to balance things out.
So in the next generation maybe only 10% are BB, 50% are Bb and 40% are bb- already we're losing lots of B alleles.
If you had lots of alleles for a gene, and one was already quite rare, it could have been lost by this stage- if you've got 20 individuals, and the allele is present in 5% of individuals, that's only one individual with the allele. In a population of 1000 that's 50 individuals with the allele, so it has a much greater chance of being passed on.