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Mutation, cell division and cancer

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Which change preserves the downstream reading frame most directly?

  1. Insertion of one coding base
  2. Deletion of three consecutive coding bases
  3. Deletion of two coding bases
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Deletion of three consecutive coding bases

It can remove one amino-acid position without shifting all later triplet grouping, although the protein may still be affected.

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Which changes the number of a particular whole chromosome?

  1. Trisomy 21
  2. A base substitution in one gene
  3. An inversion within chromosome 2
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Trisomy 21

There are three copies of chromosome 21.

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Which molecular change is central to the classic sickle-cell example?

  1. Valine is replaced by the charged amino acid glutamate.
  2. A frameshift changes every downstream beta-globin codon.
  3. A charged glutamate is replaced by non-polar valine.
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A charged glutamate is replaced by non-polar valine.

The changed side-chain property contributes to abnormal intermolecular association.

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Which statement best supports informed consent?

  1. Share the result freely with anyone who asks.
  2. Hide uncertainty so the choice feels simpler.
  3. Explain the test limits and possible choices before testing.
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Explain the test limits and possible choices before testing.

Understanding and voluntariness are central.

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What separates during mitotic anaphase?

  1. Each chromosome splits into two unreplicated halves before S phase.
  2. Sister chromatids
  3. The two DNA strands within each chromatid
  4. Homologous chromosome pairs while sisters remain joined
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Sister chromatids

They become daughter chromosomes moving to opposite poles.

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In a root-tip squash, 40 of 400 cells are in mitosis. After a drug treatment, 4 of 400 are. Which conclusion is best supported?

  1. The drug killed 90% of the root-tip cells.
  2. The drug reduced the proportion of cells dividing.
  3. The drug made mitosis happen ten times faster.
  4. The drug doubled the length of the cell cycle.
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The drug reduced the proportion of cells dividing.

The mitotic index fell from 10% to 1%, so fewer cells were in mitosis at that moment.

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Which event directly halves the chromosome-set number?

  1. Sister chromatid separation in meiosis II
  2. Replication in S phase
  3. Separation of homologues in meiosis I
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Separation of homologues in meiosis I

Each product receives one chromosome from each homologous pair.

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Which statements are true of meiosis I but NOT of mitosis? 1: Homologous chromosomes pair. 2: Sister chromatids separate. 3: Crossing over occurs. 4: The chromosome number is halved.

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

Pairing, crossing over and halving happen in meiosis I. Sister chromatids separate in mitosis and meiosis II, not meiosis I.

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At the end of normal meiosis from a diploid cell, the products are...

  1. diploid clones because two S phases occurred.
  2. haploid clones because meiotic recombination never occurs.
  3. haploid with genetic combinations that can differ.
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haploid with genetic combinations that can differ.

Homologue separation reduces ploidy and meiotic processes generate variation.

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Which pairing is correct?

  1. p53 loss of protective function; ras gain of growth-promoting activity
  2. p53 loss of a growth signal; ras gain of checkpoint arrest
  3. p53 gain of normal protective function; ras complete loss of all signalling
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p53 loss of protective function; ras gain of growth-promoting activity

These illustrate loss of restraint and inappropriate positive signalling.

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Which most directly describes metastasis?

  1. Cancer cells establishing a secondary tumour at a distant site
  2. A primary tumour increasing in size without leaving its original site
  3. New capillaries forming within a growing primary tumour
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Cancer cells establishing a secondary tumour at a distant site

This requires invasion, transport and successful colonisation.

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Write a short answer, then compare it with a sample and check for missing ideas.

Question 1 of 10

Read a DNA-content profile

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Invented flow cytometry results for 10,000 cells. Untreated: 6,000 cells at 2C, 1,500 between 2C and 4C, 2,500 at 4C. Treated with drug X: 2,000 at 2C, 1,000 between, 7,000 at 4C. (a) State the stage or stages represented by each group. (b) Calculate the percentage of cells at 4C before and after treatment, and the percentage change. (c) Suggest where drug X acts and explain how it could slow a tumour. (d) Describe how you would confirm this with a root-tip squash. [4]

2C = G1, between = S, 4C = G2 and mitosis. Percentage change uses the untreated value.

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