There may be many alleles of a single gene
A single gene can exist in more than two versions, called alleles. Human blood group is a classic example — one gene has three different alleles.
Real World
The ABO blood group gene on chromosome 9 has three alleles — Iᴬ, Iᴮ, and i — which is why blood banks like the NHS Blood and Transplant service must test donors carefully, as the combinations produce four different blood types.
Exam Focus
Use correct superscript notation (Iᴬ, Iᴮ, i) in crosses — examiners penalise inconsistent or ambiguous allele symbols.
Evaluation Scaffold
A four-step framework for high-quality evaluation. Use this for 'assess', 'evaluate', and 'to what extent' questions.
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