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Cell and Nuclear Division · Paper 2 — Free Biology HL Practice Questions
1MasterySAQ-SPhases of mitosis and meiosis5 marksPaper 2~8 min
In a laboratory, a culture of human skin cells is treated with a chemical that prevents the formation of spindle fibres during mitosis.
(a)
Describe what would happen to the chromosomes during anaphase in these treated cells. [2 marks]
(b)
The cell cycle of untreated skin cells lasts 24 hours. After treatment, 40% of cells fail to complete mitosis and undergo apoptosis; the remaining cells divide normally. A sample initially contains 800 cells. Calculate the number of cells expected after one full cell cycle. Show your working. [3 marks]
Solutions
2ChallengeSAQ-LMitosis vs meiosis7 marksPaper 2~11 min
In Drosophila melanogaster the diploid chromosome number is $2n = 8$. A geneticist studies a temperature-sensitive mutation that causes complete failure of spindle fibre formation at the restrictive temperature (). Cells are assumed to begin G1 of the cell cycle before entering division.
(a)
Calculate the number of chromosomes and the number of DNA molecules present in a single cell at each stage below, at the restrictive temperature.
- (i) At the end of mitosis, after cytokinesis has failed (spindle fibres did not form; chromatids did not separate).
-
(ii) At the end of meiosis I, after cytokinesis has occurred (spindle fibres did not form in meiosis I). -
(iii) In a cell that has completed S phase (DNA replication) and entered G2, but has not yet undergone any division. [3 marks]
(ii) At the end of meiosis I, after cytokinesis has occurred (spindle fibres did not form in meiosis I). -
(iii) In a cell that has completed S phase (DNA replication) and entered G2, but has not yet undergone any division. [3 marks]
(b)
Explain why failure of spindle fibre formation produces different chromosomal outcomes in mitosis compared to meiosis I, even though the same molecular mechanism is disrupted. [2 marks]
(c)
Evaluate the usefulness of this temperature-sensitive mutant strain for investigating the role of meiosis in generating genetic variation compared with mitosis. [2 marks]
Solutions
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