Follow the broken piece to where it lands
- The idea
- Predict
- See it
- Why
- Check
The idea
“If a chromosome loses a piece, it's a deletion. If one gains a piece, it's a duplication.”
You probably looked at one chromosome at a time. One got shorter and one got longer, so deletion and duplication both seem to fit.
The short version
The mistake: If a chromosome loses a piece, it's a deletion. If one gains a piece, it's a duplication.
What's actually true: A piece that moves onto a chromosome from another pair is a translocation, and the cell keeps every gene.
- Name the change by what happens to the broken piece. A lost piece is a deletion. A piece copied so it appears twice is a duplication.
- A piece that flips and rejoins the same spot is an inversion. That stretch keeps the same genes, but in reverse order.
- A piece that joins a nonhomologous chromosome, one from another pair, is a translocation. One chromosome loses it and the other gains it, so no genes are lost or added.
On the exam: Follow the broken piece. If it lands on a chromosome from another pair, it's a translocation.