IGCSE Biology glossary
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 alternative form of a gene, found at the same position on a chromosome. For example, the gene for seed shape has a round allele and a wrinkled allele.
What to include in an exam answer
Do not use 'gene' and 'allele' interchangeably in genetics answers. Mark schemes check. A gene codes for a characteristic; alleles are its versions. Genetic cross questions are marked on correct allele notation (R and r, defined in your answer).
Example in context
In a genetics answer: 'The gene for seed shape has two alleles, a round allele (R) and a wrinkled allele (r), found at the same position on the chromosome.'
Related syllabus topic
Inheritance