Copying DNA doesn't mix alleles
- The idea
- Predict
- See it
- Why
- Check
The idea
“When DNA is copied before meiosis, the copies can come out with new mixes of alleles.”
Replication comes right before meiosis, and meiosis makes variety, so the two blur together. Copying keeps the alleles as they are.
The short version
The mistake: When DNA is copied before meiosis, the copies can come out with new mixes of alleles.
What's actually true: Copying keeps alleles in the same order. Crossing over, independent assortment and fertilization make the new mixes.
- Each new DNA strand is built by base pairing against an old one, so a copy has the same alleles in the same order.
- Rare copying errors are mutations, which can create new alleles. They don't reshuffle the alleles a cell already has.
- Reshuffling comes later. Crossing over swaps segments between homologs, each pair sorts independently of the others, and fertilization joins two parents' gametes.
On the exam: Copying keeps alleles as they were. New mixes come from crossing over, assortment and fertilization.