Every gene and offspring needs its own factor
- The idea
- Predict
- See it
- Why
- Check
The idea
“Once I've found the chance for the gene that seems to matter, that's my answer.”
Each gene feels like its own small problem, so solving one feels like finishing. When the missing factor is a big one like 3/4, dropping it looks harmless.
The short version
The mistake: Once I've found the chance for the gene that seems to matter, that's my answer.
What's actually true: When an outcome needs several independent events, its chance is the product of their chances, one factor for each.
- When an outcome needs several independent events at once, multiply their chances. That's the product rule.
- Before you multiply, list what the outcome needs: each gene it names and each offspring it counts. Each gets a factor, even a likely one like 3/4.
- Genes on different chromosomes assort independently, and each child comes from its own fertilization. Linked genes close together on a chromosome don't follow this rule.
On the exam: List every gene and every offspring the outcome needs. Give each one a factor, then multiply.