Question

Write a short note on polyembryony?

Answer 1

Hint: The process of formation of two or more embryos from a single fertilized egg is known as polyembryony. In the case of humans, it results in the formation of two identical twins. This process of polyembryony is found both in plants and animals.The best example of Polyembryony in the animal kingdom is the nine-banded armadillo which is a medium-sized mammal. It is found in certain parts of America and thus wild species give birth to identical quadruplets.

Complete Answer:
Classification of polyembryony:
The Ernst and Schnarf classified the polyembryony into two types:
1) True polyembryony
2) False polyembryony

TRUE POLYEMBRYONY may be subdivided into two types:
A) Cleavage polyembryony
B) Adventives polyembryony

1) True polyembryony-The formation of embryos within a single embryo sac is called true polyembryony.
A) Cleavage polyembryony: The formation of an embryo within an embryo sac by the cleavage of egg or from the synergids antipodals or endosperms.
B) Adventives polyembryony: The embryo arises from the tissue lying outside the embryo sac.

2) False Polyembryony: The process of formation of two or more embryos as a result of the development of the monosporic embryo sac.

Causes of polyembryony: Some of the important theories are
(i) NECROHORMONE THEORY: According to this, the degenerating cells of nucleus act as a source of stimulus to form adventive embryos.
(ii) HYBRIDIZATION THEORY: The occurrence of multiple embryos is due to hybridization.

Importance of Hybridization:
- It is used for plant breeding and horticulture.
- It is used for the propagation of fruit trees such as citrus and mango.
- Adventive embryos play an important role to provide genetically uniform seedlings in fruit trees.
- It is used for the development of homozygous diploids.

Note: Polyembryony has ecological importance because it increases the probability under different conditions. Nuclear Polyembryony plays an important role in raising virus-free clones of polyembryonic citrus species in nature.