Science · Grades 8–12
Genetics: model crosses and their limits · Revision card
These questions use one gene with two alleles, A and a, and complete dominance where stated.
Understand the idea
Use an explicit model
These questions use one gene with two alleles, A and a, and complete dominance where stated.
Probability is not a quota
A predicted fraction does not guarantee exact counts in a small family or sample.
Traits can be complex
Real traits may involve many genes and environmental factors.
Worked examples
In the stated two-allele model, which genotype is heterozygous?
Aa contains two different alleles at the modeled locus.
Aa
For Aa × aa, what fraction of offspring is expected to be aa under the simple model?
The first parent contributes A or a equally; the second contributes a.
1/2
Explain without looking
- Explain why a dominant allele is not necessarily more common in a population.
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Preview material · independent educational review required. Grade bands are approximate, not official curriculum alignment.