Genotype vs Phenotype and Dominant vs Recessive Alleles
Genotype, phenotype, dominant and recessive alleles explained with two worked examples.
The key terms
- Genotype = the allele letters (Bb)
- Phenotype = the trait you see
- Dominant (B) shows if even one copy is present
Recessive traits show only with two copies (bb).
Example 1
Brown eyes (B) are dominant to blue (b). What is the phenotype of Bb?
- Bb has one dominant allele
- The dominant allele is expressed
Brown eyes
Example 2
Which genotypes give blue eyes?
- A recessive trait needs two copies
- Only b + b works
bb
Common mistake
Dominant means more common or stronger
Dominant only means it masks the recessive allele.
Heterozygous (Bb) and homozygous dominant (BB) look identical.
Want more Biology practice?
The free Biology study guide has quizzes, flashcards and practice exams. 100% free, no sign-up needed.
Open the Biology guide