How many meiotic and mitotic divisions need to occur for the development of a mature female gametophyte from the megaspore mother cell in an angiosperm plant?

To understand the number of meiotic and mitotic divisions required for the development of a mature female gametophyte (embryo sac) from a megaspore mother cell (MMC) in angiosperms, let us break down the process step-by-step:

1. Megasporogenesis (Meiosis):
The megaspore mother cell (MMC) is a diploid ($2n$) cell located in the nucellus of the ovule.
The MMC undergoes 1 meiotic division (meiosis) to produce a linear tetrad of four haploid ($n$) megaspores.
In most angiosperms (monosporic development, e.g., Polygonum type), three of these megaspores degenerate, and only one functional megaspore remains.

2. Megagametogenesis (Mitosis):
The single functional haploid megaspore undergoes sequential mitotic divisions (karyokinesis without immediate cytokinesis) to form the mature embryo sac:
• First Mitosis: The nucleus of the functional megaspore divides mitotically to form 2 nuclei, which move to opposite poles.
• Second Mitosis: Both nuclei divide, resulting in a 4-nucleate stage (2 nuclei at each pole).
• Third Mitosis: These 4 nuclei divide once more, producing an 8-nucleate stage (4 nuclei at each pole).
Thus, a total of 3 mitotic divisions (mitosis) occur.

3. Maturation:
After the three mitotic divisions, the 8 nuclei undergo organization and cell wall formation (cytokinesis) to form the typical 7-celled, 8-nucleate mature female gametophyte (embryo sac), which consists of a 3-celled egg apparatus, 3 antipodal cells, and 1 central cell containing 2 polar nuclei.

Therefore, the development of a mature female gametophyte from the megaspore mother cell requires 1 Meiosis and 3 Mitosis divisions.