Lesson 3.4.1.1

3.4.1.1 DNA, genes, loci and chromosomes Quiz: AQA Biology, Unit 4

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.4.1.1, DNA, genes, loci and chromosomes: 20 multiple choice questions for the AQA Biology (7402), Unit 4: Genetic information, variation and relationships, written with Revision Ninja.

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The 20 questions

  1. What is a gene?

    • A base sequence of DNA that codes for a polypeptide or a functional RNA.
    • A short circular DNA molecule found only in mitochondria and chloroplasts.
    • A single amino acid joined to a tRNA molecule in the ribosome during translation.
    • A complete set of chromosomes found in every cell of a multicellular organism.

  2. What is a locus?

    • The complete set of genes present in a cell at one time.
    • The fixed position of a gene on a particular DNA molecule.
    • The sequence of three bases that codes for a specific amino acid.
    • The loose coil of DNA associated with histone proteins in the nucleus.

  3. How are DNA molecules arranged in the nucleus of a eukaryotic cell?

    • Short, circular molecules that are not associated with any protein in the nucleus.
    • Long, linear molecules associated with histone proteins to form chromosomes.
    • Long, circular molecules arranged as plasmids that are copied during binary fission.
    • Short, linear molecules that lie free in the cytoplasm and are not bound to proteins.

  4. Which statement describes the DNA found in mitochondria and chloroplasts?

    • It is made of RNA rather than DNA and is always spliced before use.
    • It is short, circular and not associated with protein, like prokaryotic DNA.
    • It is absent from these organelles, which rely on DNA from the nucleus only.
    • It is long, linear and associated with histone proteins, like nuclear DNA.

  5. A triplet of DNA bases codes for what?

    • One intron that is removed from the gene.
    • A whole polypeptide chain.
    • A single nucleotide of mRNA.
    • A specific amino acid.

  6. Which three properties describe the genetic code?

    • Random, unstable and found only in the nucleus.
    • Linear, overlapping and specific to each species.
    • Universal, non-overlapping and degenerate.
    • Circular, spliced and dependent on histone proteins.

  7. What does it mean for the genetic code to be described as degenerate?

    • Bases can be read in more than one overlapping frame to make the same amino acid.
    • Each triplet codes for a different amino acid, with no duplication anywhere in the code.
    • More than one triplet can code for the same amino acid.
    • The code breaks down over time, so some triplets stop coding for amino acids.

  8. Which parts of eukaryotic nuclear DNA are described as exons and introns?

    • Exons are found only in prokaryotes, while introns are found only in eukaryotes.
    • Exons code for amino acid sequences, while introns are non-coding sequences within a gene.
    • Exons are the histone proteins, while introns are the DNA strands that wind around them.
    • Exons are non-coding sequences between genes, while introns code for amino acids.

  9. Which feature of eukaryotic nuclear DNA is shown by non-coding multiple repeats of base sequences?

    • They code for amino acid sequences that are used during translation in the ribosome.
    • They are the only sequences that are copied during binary fission in prokaryotes.
    • They are found between genes and do not code for polypeptides.
    • They are found inside every codon and specify which amino acid is added next.

  10. A gene is found at locus X on chromosome 5. What does this tell us about the gene?

    • It occupies a fixed position on a particular DNA molecule, which is part of chromosome 5.
    • It is located on a DNA molecule that lies free in the cytoplasm and not in a chromosome.
    • It can move freely along the chromosome, so its position changes during every cell division.
    • It is a copy of a plasmid that has been inserted into the chromosome from another cell.

  11. Why is most of the DNA in a eukaryotic nucleus described as non-coding?

    • It is removed from the nucleus before translation takes place on the ribosomes.
    • It codes only for histones, which package the DNA into chromosomes in the nucleus.
    • Much of it consists of repeats between genes and introns that do not code for polypeptides.
    • It has been lost during the formation of chromosomes, leaving only the genes behind.

  12. A student claims that every gene codes for a polypeptide. Evaluate this claim.

    • The claim is correct, because every gene in every organism codes for a polypeptide alone.
    • The claim is correct, because RNA molecules are not coded for by any region of DNA.
    • The claim is incorrect, because some genes code for functional RNA such as rRNA or tRNA.
    • The claim is partly correct, because only genes in prokaryotes code for polypeptides.

  13. A eukaryotic gene is 1200 base pairs long, and exons make up 600 of these base pairs. How many base pairs are in introns?

    • 600
    • 0
    • 300
    • 1200

  14. A coding strand has 60 bases and no stop codons. What is the maximum number of amino acids it could code for?

    • 60
    • 30
    • 20
    • 180

  15. Why does the base sequence of each gene carry the coded information for protein synthesis?

    • The base sequence determines the colour of the cell membrane and its fluidity.
    • The base sequence is the same in every gene, so it codes for the same protein each time.
    • The base sequence determines the number of ribosomes that will be made in the cytoplasm.
    • The sequence of bases determines the order of amino acids in the polypeptide.

  16. Why is the genetic code described as providing indirect evidence for evolution?

    • The same code is used by all organisms, which suggests they share a common ancestor.
    • The code changes in every generation, which shows evolution is occurring in all species.
    • The code contains only introns, which show that all species lost their exons over time.
    • Different organisms use different codes, which shows each species evolved independently.

  17. Which statement about nuclear and organelle DNA is best supported by the specification?

    • Nuclear DNA is linear and associated with histones, while organelle DNA is short, circular and not associated with protein.
    • Nuclear DNA is circular and not associated with protein, while organelle DNA is linear.
    • Nuclear DNA and organelle DNA are both short, circular and found free in the cytoplasm.
    • Nuclear DNA and organelle DNA are both linear and both associated with histone proteins.

  18. A researcher compares two genes at the same locus in two individuals of the same species. What does this comparison reveal?

    • Differences in the number of ribosomes that each individual has in the cytoplasm.
    • Differences in the sequence of histone proteins that package the DNA in each cell.
    • Differences in the codons that the same tRNA molecule can carry in each cell.
    • Differences in base sequence between alleles of the same gene at one locus.

  19. Which statement about the triplet code is correct?

    • Each triplet codes for a single base, so a sequence of four bases codes for four amino acids.
    • Each triplet overlaps with the next, so each base is part of two different amino acid codes.
    • Each triplet is read in a random order, so the amino acid sequence cannot be predicted.
    • Each triplet is read in a fixed order without overlapping with the next triplet on the mRNA.

  20. A researcher finds that a gene is 900 base pairs long. What is the maximum number of codons it can contain?

    • 450
    • 900
    • 150
    • 300

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