Dominant and recessive alleles
A dominant allele shows with one copy; a recessive needs two.
The common mistake
Thinking dominant means more common, or that a heterozygote shows a blend.
Instead: Dominant shows whenever present (Bb shows B). Recessive only shows as bb. Dominance says nothing about how common a trait is.
Worked example with Guide me
Is a person with genotype Tt tall or short, if T (tall) is dominant?
- Sugar · Is the dominant allele present?Student · Yes, T.
- Sugar · So which trait shows?Student · Tall.
Answer: Tall
Try 3 practice questions
1. What does homozygous recessive look like in letters?
Show answer
Two lowercase, e.g. tt
2. Can two brown-eyed parents have a blue-eyed child?
Show answer
Yes, if both are Bb
3. What is a heterozygote?
Show answer
Two different alleles, e.g. Bb
Quick answers
- What is the most common mistake with dominant and recessive alleles?
- Thinking dominant means more common, or that a heterozygote shows a blend.
- How do I get dominant and recessive alleles right?
- Dominant shows whenever present (Bb shows B). Recessive only shows as bb. Dominance says nothing about how common a trait is.
- Can you show a worked example?
- Is a person with genotype Tt tall or short, if T (tall) is dominant? Tall
Related concepts
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