Inbreeding pairs up alleles. It doesn't erase or damage them
- The idea
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- Why
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The idea
“Inbreeding damages DNA or wipes out good alleles, so the allele frequencies change.”
Inbred animals often have defects, so it's natural to picture their DNA getting worse. The alleles behind those defects were there all along, hidden.
The short version
The mistake: Inbreeding damages DNA or wipes out good alleles, so the allele frequencies change.
What's actually true: Inbreeding makes offspring homozygous more often, which exposes hidden harmful recessives without changing allele frequencies.
- Inbreeding is mating between relatives, and selfing is the extreme case. Relatives often carry the same alleles, so their offspring are more likely to be homozygous.
- Selfing an Aa plant gives 1/4 AA, 1/2 Aa and 1/4 aa. That is still half A and half a, so inbreeding by itself leaves allele frequencies the same.
- Many harmful alleles are recessive and stay hidden in heterozygotes. Inbreeding pairs them up, so more offspring show the defect. This is inbreeding depression.
- No DNA is damaged. Selection may later remove some aa individuals, but only after inbreeding exposed them.
On the exam: Inbreeding changes how alleles are paired, not which exist. Expect more homozygotes and recessive traits.