Question

In the case of polyembryony an embryo A develops from the synergids and the embryo B develops from the nucellus. State the ploidy of embryo A and B

Answer 1

Hint: The ploidy of an embryo depends on the ploidy of the cell from which it is developed. The synergid cells have half the usual number of chromosomes in it and the nucellus has a paired chromosome in it.

Complete answer:
The synergids are haploid in nature and therefore the nucellus is found within the integumentary region and has abundant reserve food materials. It's diploid in nature. This suggests that embryo A that develops from the synergids will have a ploidy of n and embryo B that develops from the nucellus will have a ploidy of 2n.

Additional Information: Synergid is one of two small, short-lived nuclei which is present near the egg in the mature embryo sac of a flowering plant. The synergids are the part of the egg apparatus that helps in guiding the pollen nucleus towards the egg cell for the process of fertilization. On the other hand, the nucellus is the central cellular mass of the body of the ovule, containing the embryo sac. In seed plants, the ovule is that the structure that provides rise to and contains the feminine reproductive cells. It consists of three parts that are the integument, which forms its outer layer, the nucellus, and therefore the female gametophyte in its center. In gymnosperms, it's seen that three of the four haploid spores produced in meiosis typically degenerate, leaving one surviving megaspore inside the nucellus.

Note: After fertilization, the nucellus may develop into the perisperm in the seed that feeds the embryo. In some plants, it is seen that the diploid tissue of the nucellus can also give rise to the embryo within the seed by a special mechanism of asexual reproduction called nucellar embryony.