IGCSE Biology glossary
Dominant allele
Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Definition
An allele that is expressed in the phenotype when only one copy is present (in the heterozygous condition).
What to include in an exam answer
Mark schemes reward 'expressed when one copy present' or 'expressed in the heterozygote'. Avoid 'stronger allele'. Strength language never scores and signals weak understanding to the examiner.
Example in context
Explaining a pedigree: 'The allele is dominant because it is expressed in the heterozygous condition, when only one copy is present.'
Related syllabus topic
Inheritance