IGCSE Biology glossary
Carrier
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Definition
An individual who is heterozygous for a recessive genetic condition, carrying one copy of the recessive allele but not showing the condition because the dominant allele masks its effect. Carriers can pass the recessive allele to their offspring.
What to include in an exam answer
Carriers are always heterozygous. In sex-linked conditions, only females can be carriers (e.g. XHXh for haemophilia) because males with one recessive allele express the condition.
Example in context
Explain how two parents who do not have cystic fibrosis can have a child with the condition (3 marks): Both parents are carriers (heterozygous, Ff). Each parent can pass on the recessive allele (f) to their child. If the child inherits the recessive allele from both parents (ff), they will have cystic fibrosis.
Related syllabus topic
Inheritance