Definition:

The condition of two or more embryos growing from a single fertilized egg is known as Polyembryony. The embryos are identical but genetically different from the parents because they are produced from the same egg. Between Polyembryony and the process of budding and ordinary sexual reproduction, the genetic difference between the child and the parents, but the similarity among siblings, are major distinctions. Polyembryony can occur in humans, resulting in identical twins, but it is rare and occurs at random. Polyembryony is common in many vertebrates, invertebrates, and plant species. simple polyembryony is found.

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A brief outline

Male sperm cells unite with an ovule in plants, which develops into seeds/seeds. Each seed has an embryo inside it (which is a tiny undeveloped plant). Fertilization in animals can take place both internally and externally. The male gamete fertilizes the eggs of female organisms, creating the embryo’s main nucleus. Polyembryony is defined as clonal development in which a single egg produces two genetically identical children. It can be discovered in both plants and mammals.

Polyembryony is a sort of apomixes in which embryos develop autonomously in an asexual fashion, with progenies that are genetic duplicates of the mother plant. In plants, Polyembryony takes the form of facultative apomixis. Numerous embryos of somatic origin co-exist in the same seed carrying a sexual embryo resulting from self or cross-pollination. Although various plants exhibit Polyembryony, nothing is known about the origins of this reproductive phenomenon.

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Important concepts

Polyembryony Classification

Plants with Polyembryony

Polyembryony is the formation of two or more embryos from a single seed or fertilized egg. This occurrence occurs in plants due to the fertilization of one or more embryonic sacs or the genesis of embryos outside of the embryonic sac. Antonie van Leeuwenhoek found these natural phenomena in Citrus plant seeds in 1719.

Polyembryony Types

Polyembryony can be divided into two types:

1. Polyembryony Induced – Polyembryony that has been induced experimentally
2. Spontaneous Polyembryony is a type of Polyembryony that occurs naturally.

Polyembryony can be divided into three categories, according to Webber:

1. Cleavage Polyembryony: This type of Polyembryony occurs when a single fertilized egg produces several embryos.
2. Simple Polyembryony: A number of embryos develop due to the fertilization of multiple archegonia in this type of Polyembryony.
3. Rosette polyembryony: In certain gymnosperms, additional embryos emerge from the rosette cells; this type of Polyembryony is known as rosette polyembryony.

Polyembryony in Different Gymnosperm Groups

• Cycadales have Polyembryony.

Polyembryony is a rare occurrence in Cycadales. On the other hand, Rao discovered simple Polyembryony in Cycas Circinalis in 1964. Two neighboring archegonia of the same ovule grow independently into two embryos and, on rare occasions, two seedlings in this species.

• Coniferous Polyembryony

Simple Polyembryony occurs in most Coniferales members, with the number of embryos ranging from two to numerous. Cleavage polyembryony has been reported in Pinaceae, Taxodiaceae, Cupressaceae, and Podocarpaceae families. Both simple and cleft Polyembryony are frequent in Cupressus.

• Taxales Polyembryony

Taxus’ female gametophyte contains a variety of archegonia. The fertilization of several archegonia eggs results in simple Polyembryony. However, just one embryo out of a large number matures. Suspensor cell cleavage occurs. The rosette embryos are these clusters of cells. These embryos, on the other hand, do not develop further.

• Gnetales Polyembryony

Polyembryony is found in all Gnetales. In Gnetum, Polyembryony is discovered to be of a very high order. Each seed in this group contains several prothalli and zygotes, and the multiplication of embryos from each zygote is due to the branching of the principal suspensors.

Polyembryony Causes

Different theories have been proposed to explain Polyembryony –

• Theory of Necrohormones

Nucellus degeneration occurs in cells to stimulate surrounding cells to divide. It results in the development of adventive embryos.

• Theory of Hybridization

The recombination of genes occurs during the hybridization process, resulting in the formation of a single unit, which produces many embryos.

Significance of Polyembryony in NEET exam

In the NEET test for the year 2020, almost 5% of questions came from the Sexual Reproduction in Flowering Plants chapter. In 2021, it was worth noting that this chapter’s apomixis and polyembryony topic accounted for roughly 6.6 percent of questions.

Also read Important Topic Of Biology: Fragmentation.

FAQs

What are the causes of polyembryony?

The exact cause of polyembryony is not known, but it is thought to be related to environmental conditions and genetic factors. In some cases, it is believed that a single egg contains multiple sets of chromosomes from different parents. In other cases, polyembryony can be triggered by environmental conditions such as temperature or light. It can also be induced artificially, through techniques such as cloning or genetic engineering.

What are the benefits of polyembryony ?

Polyembryony can provide certain advantages in some species of animals. For example, it can increase the genetic diversity of a population, allowing for a greater variety of traits to be expressed. It can also help species to adapt to changing environmental conditions, as multiple embryos can provide a greater chance of survival for some species.

What are the disadvantages of polyembryony?

The main disadvantage of polyembryony is that it can lead to the production of unhealthy offspring. Multiple embryos can be more prone to birth defects and other health problems due to the increased genetic variability. This can affect the long-term survival of a species.

Are there any safety concerns related to polyembryony?

Yes, there are safety concerns related to polyembryony. Artificial induction of polyembryony can be risky, as it can cause genetic mutations or other unintended consequences. It is important to conduct thorough research before attempting to induce polyembryony artificially.