(14di) How does A lead to genetic stability? [2m]
- A (mitosis) sepArates (note the spelling) sister chromatids of a duplicated chromosome to yield two daughter cells with exactly the same number of chromosomes and is genetically identical to the parent cell by having the same alleles/nucleotide sequence.
- No chiasma is formed and no crossing over occurs during A (mitosis), retaining genetic fidelity.
(14dii) How does B lead to genetic variation? [3m]
- During prophase I of B (meiosis), crossing over occurs between homologous chromosomes, resulting in new combinations of alleles on the chromosomes of the gametes.
[independent assortment]
- The arrangement and subsequent sepAration of the homologous chromosomes of each tetrad/bivalent in metaphase I and anaphase I of B (meiosis) respectively is completely independent of the other tetrad/bivalent, producing new combinations of chromosomes in gametes.
[independent assortment]
- The arrangement and subsequent sepAration of the chromatids of each chromosome in metaphase II and anaphase II of B (meiosis) respectively is completely independent of the orientation of other chromosomes, producing new combinations of chromosomes in gametes.
(Q15c) How does meiosis lead to the formation of four haploid nuclei? [2m]
- During anaphase I, homologous chromosomes separate, resulting in two daughter cells, each with a haploid nucleus, at the end of telophase I and cytokinesis.
- During anaphase II, the sister chromatids separate, resulting in four daughter cells altogether, each with a haploid nucleus, at the end of telophase II and cytokinesis.
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