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Q.What will be the ploidy of the cells of the nucellus, MMC, the functional megaspore and female gametophyte?

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Nucellus and MMC are diploid (2n, ordinary sporophyte tissue); the functional megaspore and the female gametophyte it produces are both haploid (n) — the ploidy switches exactly at meiosis, and stays haploid afterward.

Tracking ploidy through the whole sequence in §1.2.2:

  1. Nucellus — diploid (2n). The nucellus is ordinary tissue of the ovule (the sporophyte generation), formed by normal mitotic divisions like the rest of the plant body. No meiosis has happened yet.
  2. Megaspore mother cell (MMC) — diploid (2n). The MMC differentiates from a nucellar cell — it is still sporophyte tissue at this point, so it is also diploid, right up until it enters meiosis.
  3. Functional megaspore — haploid (n). The MMC undergoes meiosis, producing four megaspores; each is haploid, since meiosis is the chromosome-halving division. Only one of these four survives (the other three degenerate) — this one surviving cell is the functional megaspore, and it is haploid. …

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