Have you ever wondered why identical twins are born or why identical twins are identical? Polyembryony is the mechanism by which humans can produce identical twins. ‘Poly’ means many and “embryony” means embryo. Understanding Polyembryony, its types, occurrences, and significance will be easier if you read and understand this article.

What is Polyembryony and how does it occur?

It is the development of more than one embryo in a single ovule or seed or the complete cleavage of an ovule after fertilisation that is referred to as polyembryony. Due to this phenomenon, the development of supernumeraries of various frequencies, such as the doublet, triplet, quadruplet, quintuplet, and sextuplet (among others), is possible.

Humans can produce identical twins, it is due to polyembryony. The presence of this compound in both animals and plants is possible.

Plants and Polyembryony

It was Antoni van Leeuwenhoek who discovered this phenomenon in orange seeds for the first time. Gymnosperms have such a high frequency of polyembryony that it could be considered a distinguishing characteristic of this group. Women gametophytes develop two or more arches in the majority of gymnosperms that have polyembryony in their reproductive organs. Because each archegonium contains an egg, the presence of multiple archegonium results in the fertilisation of two or more eggs, resulting in the formation of two or more possible embryos in the process.

Types of Polyembryony

It is important to note that there are two different types of polyembryony, which are as follows:

1. Artificially Induced Polyembryony: Examples of polyembryony that have been induced artificially are included in this category.
2. Spontaneous Polyembryony: This term refers to any case of naturally occurring polyembryony that occurs without the intervention of a medical professional.

It is possible to differentiate between three types of polyembryony:

1. Cleavage Polyembryony:

A cleavage polyembryony is when a young embryo or zygote divides into two or more units. It is also referred to as zygote cleavage or budding. These units eventually develop or mature into fully functional embryos that can stand on their own. Gymnosperms are the most common species affected, while angiosperms are comparatively rare. Plant Pinus is a good example. The zygote divides twice, resulting in the formation of four nuclei.

1. Simple Polyembryony:

When more than one egg or a large number of archegonia eggs are fertilised, this is referred to as simple polyembryony. Pinus is also a good example of simple polyembryony in its most basic form.

1. Rosette Polyembryony:

For example, in some gymnosperms (e.g., a few Pinus species), additional embryos emerge from the rosette cells, resulting in a type of polyembryony known as rosette polyembryonic polyembryony.

Classification of Polyembryony

1. True Polyembryony

True polyembryony is defined as the formation of more than one embryo in the same embryo-sac of the ovule during a pregnancy. Additionally, antipodal cells or synergids are responsible for producing the additional embryo(s), which are created either through the cleavage of an egg or by the antipodal cells or synergids.

1. False Polyembryony 

False polyembryony is defined as the formation of more than one embryo in different embryo sacs within the ovule, rather than in the same embryo sac.

Polyembryony in Animals

1. The fact that an egg can produce two or more embryos under certain conditions is perhaps no more remarkable than the fact that an egg can form a single individual. A type of polyembryony known as twinning occurs in the vast majority of animals accidentally, in which a single egg splits into two or more embryos, but an obligatory form is extremely rare.
2. Twinning must be regarded as the most basic type of polyembryony because it is the most common.
3. Polyembryony can be found or observed in a wide variety of invertebrates, including cnidarians, insects, and echinoderms, among others.

What Is the Importance of Polyembryony?

1. This phenomenon is extremely important in the fields of plant breeding and horticulture. Citrus nucellar seedlings are superior clones of orchard stock when compared to cuttings in the field of horticulture.
2. Alternatively, nucellar embryos are intended to be disease-free, whereas nucellar seedlings are intended to restore the vigour that has been lost as a result of continuous cutting propagation.
3. The adventive polyembryony found in citrus and mango plants is extremely beneficial to the growth of the plants.
4. Using adventive embryos to produce genetically homogeneous fruit tree seedlings is also critical for producing genetically homogeneous fruit trees.
5. The haploids can be used to produce homozygous diploids, which are extremely valuable in many situations.

Conclusion

It is defined as the formation of multiple embryos in a single egg or seed, or by the complete cleavage of an unfertilized egg, in the course of a fertilised egg’s development. We gained a better understanding of the different types of polyembryony in plants as a result of this article. Polyembryony was once considered a negative trait, but it is now recognised as a desirable trait in citrus fruits, roses, mangoes, apples, Jamuns, almonds, and other similar fruits to produce high-quality products of genuine value. It contributes to the preservation of the resemblance between parents and children. It is possible to keep the vitality of nucellar seedlings while also keeping them disease-free.