Question

Define Apomixis and Polyembryony.

Answer 1

Hint: Asexual reproduction without fertilisation is referred to as apomixis. Polyembryony is the formation of two or more embryos from a single fertilised egg.

Complete step-by-step answer:

Apomixis- Apomixis is defined in flowering plants as the asexual formation of a seed from the maternal tissues of the ovule, avoiding the processes of meiosis and fertilisation that lead to embryo development.
i. Thus, "normal asexual reproduction" of plants, such as propagation from cuttings or leaves, was never considered apomixis, but seed replacement by a plantlet or flower replacement by bulbils were classified as types of apomixis.
ii. Offspring produced apomictically are genetically identical to the parent plant.
In flowering plants, the term "apomixis" is commonly used to refer to agamospermy or clonal reproduction via seeds.
iii. Although agamospermy may exist in gymnosperms, it appears to be absent in that group.
iv. It can be found in the Rosaceae, Asteraceae, and Poaceae families, but not in the Orchidaceae.
v. Apomixis is classified into several types based on the relative asexual mechanisms that are analogous to the sexual life cycle of flowering plants.
vi. There are two major types of apomixis:
     1. Vegetative apomixis
     2. Agamospermy.

Polyembryony- Polyembryony is a phenomenon that occurs when two or more embryos develop from a single fertilised egg.

i. It results in the formation of two identical twins in the case of humans. This phenomenon occurs in both plants and animals.
ii. The nine-banded armadillo is the best example of Polyembryony in the animal kingdom.
iii. This wild species gives birth to identical quadruplets and is a medium-sized mammal found in certain parts of America.
iv. This phenomenon occurs in plants as a result of either the fertilisation of one or more embryonic sacs or the origination of embryos outside of the embryonic sac.
v. Antonie van Leeuwenhoek discovered this natural phenomenon in Citrus plant seeds in 1719.
vi. Polyembryony is classified into two types:
1. Polyembryony that has been induced experimentally
2. Polyembryony that occurs spontaneously

Note: Apomixis is a type of reproduction in which no zygote is formed through gametic fusion. Embryos develop directly from the nucellus's diploid cells or the ovule's integuments, rather than from a fertilised egg.