A regrown population still lacks its lost alleles
- The idea
- Predict
- See it
- Why
- Check
The idea
“The population grew back, so its genetic diversity came back too.”
Big populations usually hold more variation, so a regrown crowd looks healthy. Every animal in it carries only the few survivors' alleles.
The short version
The mistake: The population grew back, so its genetic diversity came back too.
What's actually true: Genetic diversity depends on how many different alleles a population has. Regrowth only copies the survivors' alleles.
- Genetic diversity is how many different alleles a population carries and how often individuals are heterozygous. A headcount measures neither.
- A crash is a bottleneck. Most alleles are rare, so many are missing from the few survivors just by chance. This is genetic drift.
- Offspring inherit copies of their parents' alleles, so regrowth adds no new ones. New alleles come only from rare mutations or from migrants, which is gene flow.
- Until then, natural selection has less variation to act on.
On the exam: Count alleles, not individuals. A regrown population carries only the alleles its survivors had.