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GCSE Biology · key term
Having two different 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 they differ, as in Rr, it is heterozygous. Whether an organism is homozygous or heterozygous describes its genotype, not just how it looks. For example, RR and Rr have the same red phenotype in this model but different genotypes.
Specification 3.13, 3.16 · Paper 1
Having two different 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 different alleles for a gene, such as .
Specification B5.1a, B5.1i · Paper 2 (Foundation), Paper 4 (Higher)
Having two different alleles of a particular gene.
Revise: Genetic terms‘Dominant’ describes the observed phenotype of the heterozygous plant; it does not mean that one allele removes the other.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
Having two different alleles of a particular gene, such as .
Revise: Inheritance TermsAn organism could be homozygous for one gene but heterozygous for another.
A heterozygous organism still carries the recessive allele even when its phenotype shows the dominant characteristic.
A dominant phenotype does not always reveal a person’s genotype: the person may be homozygous dominant or heterozygous.
When explaining dominance, say what happens to the phenotype of a heterozygous organism. Do not say that the dominant allele prevents the recessive allele from being inherited.
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