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Mutation, cell division and cancer

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Which coding-region change most directly produces a downstream frameshift?

  1. Deletion of exactly three nucleotides.
  2. Insertion of one nucleotide.
  3. Substitution of one nucleotide with no addition or loss.
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Insertion of one nucleotide.

Codons are triplets, so one extra base changes subsequent grouping.

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Which mutation would NOT cause a frameshift?

  1. Deleting one base
  2. Inserting one base
  3. Deleting three adjacent bases
  4. Inserting two adjacent bases
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Deleting three adjacent bases

Removing three bases removes one codon; the downstream reading frame is unchanged.

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A-B-C-D becomes A-B-C-C-D. Which change is represented?

  1. Deletion.
  2. Duplication.
  3. Inversion.
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Duplication.

Segment C appears twice.

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Which causal order is appropriate?

  1. DNA substitution, loss of all haem iron, then altered cell shape.
  2. DNA substitution, changed beta-globin, altered aggregation, less flexible cells.
  3. Low oxygen causes the inherited DNA substitution in every red cell.
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DNA substitution, changed beta-globin, altered aggregation, less flexible cells.

This connects molecular information to the cellular effect.

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Which feature best supports informed consent?

  1. Telling the person that a positive screen is a certain diagnosis, so the choice is simple.
  2. Explaining limitations and allowing a voluntary decision to accept or decline.
  3. Sharing identifiable results without permission for convenience.
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Explaining limitations and allowing a voluntary decision to accept or decline.

Understanding and freedom from pressure are both needed.

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Which event normally happens before mitosis?

  1. DNA replication during S phase.
  2. A second round of replication between every mitotic stage.
  3. Separation of sister chromatids during G1.
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DNA replication during S phase.

The duplicated material is then distributed to daughter nuclei.

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What moves apart during mitotic anaphase?

  1. Both sister chromatids move together to the same pole.
  2. Paired homologous chromosomes while sisters remain joined.
  3. Chromatids stay joined while the nuclear envelope reforms around them.
  4. Sister chromatids, which become individual daughter chromosomes.
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Sister chromatids, which become individual daughter chromosomes.

Corresponding copied information is distributed to opposite poles.

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Why is tight regulation of division necessary?

  1. To prevent DNA replication during every cycle, including normal repair.
  2. To prevent inappropriate proliferation and transmission of damaged genetic material.
  3. To allow a cell to divide whenever nutrients are present, regardless of DNA damage.
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To prevent inappropriate proliferation and transmission of damaged genetic material.

Division should occur under suitable, checked conditions.

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Which event specifically indicates metastasis?

  1. Cells from a primary tumour establish a secondary tumour elsewhere.
  2. A vessel grows towards a tumour without evidence of distant cells.
  3. A cell replicates DNA normally.
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Cells from a primary tumour establish a secondary tumour elsewhere.

Spread and establishment at another site define the process.

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Which comparison is correct?

  1. Meiosis reduces chromosome number but random fertilisation removes the resulting variation.
  2. Mitosis always halves chromosome number, while meiosis preserves it.
  3. Meiosis reduces chromosome sets and generates varied combinations.
  4. Crossing over between sister chromatids in prophase II is the main source of variation.
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Meiosis reduces chromosome sets and generates varied combinations.

These are its key significance for sexual reproduction.

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Which processes produce genetic variation among offspring? 1: Crossing over in meiosis I. 2: Independent assortment in meiosis I. 3: Mitosis in the zygote. 4: Random fertilisation.

  1. 1, 2 and 4 only
  2. 1, 2 and 3 only
  3. 1, 2, 3 and 4
  4. 1 and 2 only
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1, 2 and 4 only

Crossing over, independent assortment and random fertilisation all create new combinations. Mitosis copies the genome exactly.

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Question 1 of 11

Calculate and use a mitotic index

4 marks

In an invented root-tip study, a student counts 600 cells in an untreated root and finds 45 in mitosis. In a root treated with a chemical, 18 of 600 counted cells are in mitosis. (a) Calculate both mitotic indices. (b) Calculate the percentage change in mitotic index caused by the chemical, to 3 significant figures. (c) Suggest what the chemical does to the cell cycle. (d) Describe how the distance between sister centromeres changes during anaphase. [4]

Index = cells in mitosis / total x 100. Percentage change uses the untreated value as the original.

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