Asexual lines still get new mutations
- The idea
- Predict
- See it
- Why
- Check
The idea
“New mutations only come from meiosis, so a clone copies its DNA perfectly every time.”
Meiosis gets the credit for variation, so it's easy to think mutations start there. Any cell that divides has to copy its DNA, and copying isn't perfect.
The short version
The mistake: New mutations only come from meiosis, so a clone copies its DNA perfectly every time.
What's actually true: Mutations come from DNA copying errors and damage, in any cell. Sex shuffles existing alleles into new combinations.
- A cell copies all its DNA before mitosis or binary fission. Proofreading and repair fix most copying errors, but a few slip through as new mutations.
- Cells that divide by mitosis copy their DNA too, so your skin cells collect mutations. Only mutations in cells that make offspring get passed on.
- Sex does something else. Crossing over, independent assortment and fertilization deal existing alleles into new combinations. Mutation is what makes new alleles.
On the exam: Any time DNA is copied, it can mutate. Sex shuffles alleles. Mutation makes new ones.