Gene
Exam-ready definition
A length of DNA that codes for a protein (the unit of inheritance passed from parent to offspring).
How this is marked
The Extended-level paying point is that a gene is a length of DNA that codes for a protein. Do not confuse a gene with an allele: an allele is a version of a gene. Students also lose marks writing that genes are 'found on chromosomes' as the whole answer, without saying what a gene actually is. Appears across inheritance, variation and biotechnology topics.
In an exam answer
Defining the term: 'A gene is a length of DNA that codes for a particular protein, and different forms of the same gene are called alleles.'
Full topic guide: Inheritance