Ploidy of cells in ovule development

Ovule development involves the formation of female gametophytes that produce egg cells, which are fertilized by sperm cells to form a zygote. The process starts with the formation of a megasporangium in the ovule. The megasporangium then undergoes meiosis to produce four haploid megaspores. However, only one of the megaspores survives and develops into the female gametophyte. Here we will discuss the ploidy of the cells of the nucellus, MMC, the functional megaspore, and female gametophytes.

Ploidy of the nucellus

The nucellus is the tissue that surrounds the megasporangium and provides nutrients to the developing embryo. The nucellus is diploid, i.e., it contains two sets of chromosomes. The cells of the nucellus are somatic cells, and they do not undergo meiosis during ovule development.

Ploidy of the MMC

The MMC or the megasporocyte is the cell that undergoes meiosis to produce four haploid megaspores. The MMC is also diploid, i.e., it contains two sets of chromosomes. The MMC undergoes meiosis I to produce two haploid cells, and then meiosis II to produce four haploid megaspores.

Ploidy of the functional megaspore

Out of the four haploid megaspores produced by the MMC, only one survives and develops into the female gametophyte. This surviving megaspore is called the functional megaspore, and it is haploid, i.e., it contains one set of chromosomes.

Ploidy of the female gametophyte

The functional megaspore undergoes three rounds of mitosis to produce eight haploid nuclei. These nuclei then arrange themselves to form the female gametophyte, which is also haploid. The female gametophyte contains seven cells and eight nuclei. One of the cells is the egg cell, which fuses with the sperm cell to form a zygote.

Conclusion

In conclusion, the nucellus and MMC are diploid, while the functional megaspore and female gametophyte are haploid. The haploid nature of the functional megaspore and female gametophyte is essential for sexual reproduction, as it ensures that the offspring have the correct number of chromosomes.

Nucellus - 2N (Diploid)