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GCSE Biology · key term
Having two identical alleles of a gene.
Used by AQA, Edexcel and OCR
Specification 4.6.1.6 · Paper 2
Revise: Key Vocabulary and Principles of Genetic InheritanceWhen both alleles are the same, the organism is homozygous for that gene: RR is homozygous dominant and rr is homozygous recessive. When they differ, as in Rr, it is heterozygous. Whether an organism is homozygous or heterozygous describes its genotype, not just how it looks.
Specification 3.13, 3.16 · Paper 1
Having two identical alleles for a particular gene.
Revise: Genetic TerminologyIf the alleles are the same, the genotype is homozygous; if they differ, it is heterozygous. For example, in a simple pea-plant height example, T represents an allele for tall plants and t an allele for short plants. TT and tt are homozygous; Tt is heterozygous.
Having two identical alleles for a gene, such as or .
Specification B5.1a, B5.1i · Paper 2 (Foundation), Paper 4 (Higher)
Having two identical alleles of a particular gene.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
Having two identical alleles of a particular gene, such as or .
Revise: Inheritance TermsAn organism could be homozygous for one gene but heterozygous for another.
A dominant phenotype does not always reveal a person’s genotype: the person may be homozygous dominant or heterozygous.
Apply homozygous and heterozygous to a genotype for a particular gene, not to the organism’s entire genome.
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