A smooth range in a trait takes many genes
- The idea
- Predict
- See it
- Why
- Check
The idea
“One gene with incomplete dominance can make a smooth range, like human height.”
Incomplete dominance already puts the heterozygote between its parents, so one gene seems able to fill the gap. It only adds one middle class.
The short version
The mistake: One gene with incomplete dominance can make a smooth range, like human height.
What's actually true: A smooth range comes from many genes that each add a little, blurred further by the environment.
- One gene makes a few genotypes you can count. Even with incomplete dominance or extra alleles, the phenotypes come in separate steps.
- Height is a polygenic trait, shaped by many genes that each add a small amount. More genes means more possible totals and smaller steps.
- The environment, like nutrition, nudges each individual up or down. That blurs the steps into a continuous range.
On the exam: A smooth, bell-shaped range means many genes plus environment. One gene gives classes you can count.