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AQA A-level Biology — Genetic Information and Variation flashcards

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AQA A-level Biology topic 4: genes, the genetic code, transcription and translation, mutation and meiosis, natural selection and aseptic technique (required practical 6), taxonomy, the index of diversity and measuring genetic diversity.

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Learn deck · part of AQA A-level Biology · written against: AQA AS and A-level Biology (7401/7402) specification, version 1.6, July 2026 (eight topics). Updated 2026-10-10.

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  1. How does DNA in a prokaryotic cell differ from the DNA in a eukaryotic nucleus?
    Prokaryotic DNA is short, circular and free of proteins; nuclear DNA is very long, linear and wound round proteins called histones.

    A eukaryotic DNA molecule together with its histones forms a chromosome.
    Genetic Information and Variation › DNA Genes and Chromosomes
  2. Which DNA in a eukaryotic cell resembles prokaryotic DNA?
    The DNA in mitochondria and chloroplasts: like bacterial DNA, it is short and circular, with no proteins attached.

    These organelles also have their own small ribosomes.
    Genetic Information and Variation › DNA Genes and Chromosomes
  3. How does AQA define a gene?
    A stretch of DNA whose base sequence carries the code either for a polypeptide's amino acid sequence or for a functional RNA, such as rRNA or tRNA.

    Watch out: not every gene codes for a protein.
    Genetic Information and Variation › DNA Genes and Chromosomes
  4. What is a gene's locus?
    The fixed position a gene occupies on a particular DNA molecule.

    Alleles of the same gene occupy the same locus on homologous chromosomes.
    Genetic Information and Variation › DNA Genes and Chromosomes
  5. How many DNA bases code for one amino acid, and what is the group called?
    Three bases, called a triplet.

    On mRNA the matching three bases are called a codon.
    Genetic Information and Variation › DNA Genes and Chromosomes
  6. What does it mean that the genetic code is universal?
    The same triplet codes for the same amino acid in all organisms.

    This is indirect evidence for evolution, and it lets a human gene be expressed in a bacterium. A few minor variants exist, for example in mitochondria, but AQA treats the code as universal.
    Genetic Information and Variation › DNA Genes and Chromosomes
  7. What does it mean that the genetic code is non-overlapping?
    Each base is read as part of only one triplet.

    So a substitution affects at most one codon.
    Genetic Information and Variation › DNA Genes and Chromosomes
  8. What does it mean that the genetic code is degenerate?
    Most amino acids are coded for by more than one triplet.

    There are 64 possible triplets but only 20 amino acids.
    Genetic Information and Variation › DNA Genes and Chromosomes
  9. What is the difference between introns and exons?
    Exons are the sequences in a gene that code for amino acids; introns are non-coding sequences that separate them.

    Introns are typical of eukaryotic genes; prokaryotic genes very rarely contain them.
    Genetic Information and Variation › DNA Genes and Chromosomes
  10. Apart from introns, what non-coding DNA does a eukaryotic nucleus contain?
    Base sequences repeated many times in the DNA between genes, which do not code for polypeptides (non-coding multiple repeats).

    Much of the nuclear DNA in eukaryotes does not code for polypeptides.
    Genetic Information and Variation › DNA Genes and Chromosomes

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About these cards

Review status: Second-reader reviewed, with corrections applied.

Checked against:

  • Topic outline follows the AQA AS and A-level Biology (7401/7402) specification, version 1.6 (July 2026) (outline only; no specification text reproduced).
  • OpenStax Biology 2e, consulted as a reference; no text copied.
  • Also checked against the AQA AS and A-level Biology required practical handbook, version 2.3 (January 2026) and Practical Biology (practicalbiology.org) (reference only; no text copied).

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