Homozygous
Exam-ready definition
Having two identical alleles of a particular gene.
How this is marked
The paying words are 'two identical alleles' of the same gene. Students drop the mark by writing 'two of the same gene' (it is alleles, not genes). Examiners also expect you to know that two homozygous parents of the same genotype always produce offspring with that genotype for that gene. Appears in Paper 4 genetic diagram questions.
In an exam answer
Describing a genotype: 'The plant TT is homozygous because it has two identical alleles of the gene for height.'
Full topic guide: Inheritance