Meiosis shuffles alleles. Mutation makes new ones.
- The idea
- Predict
- See it
- Why
- Check
The idea
“Meiosis makes new alleles. That's why siblings from the same parents turn out different.”
Crossing over looks like it builds something new. It does, but only new mixes of alleles the parent already had.
The short version
The mistake: Meiosis makes new alleles. That's why siblings from the same parents turn out different.
What's actually true: Meiosis sorts a parent's existing alleles into new combinations. New alleles come from mutation, a change in the DNA sequence.
- An allele is a version of a gene with its own DNA sequence, so a new allele needs a new sequence. Changing the sequence is a mutation.
- Crossing over swaps matching pieces between homologous chromosomes. In independent assortment, each pair separates on its own. Both remix alleles the cell already has.
- Mutation supplies new alleles. Meiosis and fertilization mix them into new genotypes for natural selection to act on.
On the exam: Meiosis makes new combinations of alleles. Only mutation makes a new allele.