Edexcel IGCSE Biology · Spec 3.21B
Codominance (Triple)
Codominance and how to work out genetic crosses, using human blood groups as an example.
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Codominance (Triple)
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Spec 3.21B
What you need to know
- Explain what codominance means
- Use a cross to show codominant alleles
- Predict the ratio from a codominant cross
Active recall
Quick check
Answer each question before opening the answer.
What is codominance?
When both alleles are expressed in the phenotype because neither is dominant over the other.
Give an example of codominance.
The ABO blood group system, where the I^A and I^B alleles are codominant (giving blood group AB).
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