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NCERT Exemplar · Q19

Q.In a flower, if the megaspore mother cell forms megaspores without undergoing meiosis and if one of the megaspores develops into an embryo sac, its nuclei would be:

(a) Haploid
(b) Diploid
(c) A few haploid and a few diploid
(d) With varying ploidy
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If the megaspore mother cell skips meiosis and forms a diploid megaspore, the resulting embryo sac and all its nuclei will be diploid.

In a typical flowering plant, the megaspore mother cell is a diploid cell located inside the ovule. Normally, it undergoes meiosis to produce four haploid megaspores. Three of these degenerate, and the surviving one — the functional megaspore — develops into the female gametophyte, or embryo sac. The embryo sac then undergoes mitotic divisions to produce eight haploid nuclei (the egg cell, synergids, antipodals, and the two polar nuclei). This is the standard, textbook sequence.

Now, the question asks you to imagine a scenario where the megaspore mother cell does not undergo meiosis. Instead, it simply forms megaspores through mitosis. That means each megaspore produced is genetically identical to the mother cell — and therefore diploid, not haploid. One of these diploid megaspores then develops into an embryo sac.

Since the embryo sac develops from a diploid megaspore, and all subsequent divisions inside it are mitotic (as they normally are), every nucleus in that embryo sac will also be diploid. The egg cell, the synergids, the antipodals, and the polar nuclei — all will have the same ploidy as the original megaspore mother cell. …

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