IGCSE Biology glossary
Heterozygous
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Definition
Having two different alleles of a particular gene.
What to include in an exam answer
The paying point is 'two different alleles' of the same gene. A heterozygous individual carrying a recessive allele is a carrier, and in Paper 4 you are often asked to identify carriers from a pedigree or cross. Do not write 'two different genes', and remember a heterozygote shows the dominant phenotype unless the alleles are codominant.
Example in context
Identifying a carrier: 'The genotype Tt is heterozygous because it has two different alleles of the gene, one dominant and one recessive.'
Related syllabus topic
Inheritance