A trait that skips both parents is recessive
- The idea
- Predict
- See it
- Why
- Check
The idea
“Two black mice had a white pup, so white must be the dominant color.”
A white pup in a black litter looks like white won out. It was actually there all along, hidden in both parents.
The short version
The mistake: Two black mice had a white pup, so white must be the dominant color.
What's actually true: When one allele is dominant, a trait that shows up in offspring but in neither parent is the recessive one.
- With complete dominance, one copy of the dominant allele is enough to show its trait. So any parent carrying it shows it.
- A heterozygote has one copy of each allele. It shows the dominant trait but can pass on the recessive allele.
- Two heterozygotes, Bb and Bb, have offspring about 1 BB to 2 Bb to 1 bb. That comes out 3 dominant to 1 recessive.
On the exam: A trait that was hidden in the parents and shows up in their offspring is recessive.