Describe the relationship between genes, chromosomes, DNA and the nucleus in a human body cell.

AQA A-Level Biology (7402) — 3.4.1 DNA, Genes and Chromosomes · Describe · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

The nucleus contains chromosomes.
Chromosomes are made of DNA.
DNA is a very long molecule.
A gene is a small section of DNA that is part of a chromosome.
Each gene codes for a specific protein (or a specific trait).

Examiner tips

  • Use the exact phrases from the mark scheme, e.g. "contains chromosomes" and "codes for a specific protein".
  • Show the logical order: nucleus → chromosomes → DNA → genes → proteins.
  • Keep sentences short and to the point to fit the 5‑mark limit.

Common mistakes

  • Writing "genes are in the nucleus" instead of "the nucleus contains chromosomes".
  • Confusing DNA with RNA or omitting that genes are part of chromosomes.
  • Using vague terms like "DNA is long" without specifying "very long" or "molecule".

Mark scheme (5 marks)

  1. The nucleus contains chromosomes
  2. Chromosomes are made of / consist of DNA
  3. DNA is a long molecule / DNA molecules are very long
  4. A gene is a small section of DNA / a gene is part of a chromosome
  5. Each gene codes for / determines a specific protein (or a specific characteristic / trait)

Key terms in this question

gene · chromosome · DNA · nucleus

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