Question 1

Paper 2Medium16 marks

Figure 1 shows possible chromosome outcomes in a eukaryotic species with a diploid chromosome number of 2n = 4. The parent nucleus has completed DNA replication before either pathway begins. Chromosomes of the same length are homologous; solid and dashed lines distinguish the two homologues in each pair. The central dot on each chromosome represents a centromere. Crossing-over is not shown.

replicated parentnucleusMitosisMeiosisafter meiosis Iafter meiosis II
(a)

State the number of chromosomes and the number of chromatids in the replicated parent nucleus in Figure 1.

[2]
(b)

Using Figure 1, compare the number of nuclei formed and the chromosome number per nucleus after mitosis and meiosis.

[4]
(c)

Explain the role of DNA replication before mitosis and meiosis, referring to chromatids and their separation during these processes.

[4]
(d)

Explain two processes by which meiosis can generate genetically different nuclei. Explain why nuclear division should be completed before cytokinesis.

[6]

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