Lesson · S.2.3
Mendelian inheritance
Alleles, dominant and recessive traits, and how to fill in a Punnett square to predict what offspring will look like.
ObjectiveS.2.3Read2 minExam weightBiology ≈ 20% of Science
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See editions and pricing →What you will be able to do
- Distinguish between genotype and phenotype.
- Use a Punnett square to predict offspring genotypes and phenotypes.
- Recognise a three-to-one phenotype ratio as the signature of two heterozygous parents.
What the lesson concludes
- Genotype is the pair of alleles carried; phenotype is the trait that shows.
- A dominant allele shows up whenever present; a recessive allele only shows up in a homozygous pair.
- Homozygous means matching alleles; heterozygous means one of each.
- A Punnett square crosses two parents' alleles to predict offspring genotypes.
- A three-to-one phenotype ratio signals two heterozygous parents.