Aim for FiveBiology

Conceptual analysis

When homologous chromosomes don't separate

  • Unit 5
  • 4 points
  • About 10 minutes

You can use a calculator on this question, just like on exam day.

A short question about a biological system that gets disrupted. You describe and explain the normal process, then predict what the disruption causes and justify that prediction. On the exam: Question 4 of 6 in Section II; about 10 minutes suggested.

The question

A species of plant has a diploid chromosome number of 2n = 8, made up of four pairs of homologous chromosomes. In one cell undergoing meiosis, the two chromosomes of pair 2 fail to separate in meiosis I and both move to the same pole. Meiosis II then happens normally in both cells.

Suggested time: 10 minutes

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Part (a)

1 point

Describe what normally happens to homologous chromosomes during meiosis I.

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Part (b)

1 point

Explain how normal meiosis and fertilization keep the chromosome number of this species the same from one generation to the next.

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Part (c)

1 point

Predict the number of chromosomes in each of the four gametes produced by the cell in which pair 2 failed to separate.

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Part (d)

1 point

Justify your prediction in part (c).

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