What is the Difference Between Apomixis and Polyembryony

The main difference between apomixis and polyembryony is that the apomixis is the formation of an embryo without undergoing fertilization in plants whereas, the polyembryony is the development of two or more embryos from a fertilized egg. 

Apomixis and polyembryony are two methods of reproduction found in different types of plants. Furthermore, apomixis is a form of asexual reproduction while polyembryony is a form of sexual reproduction.

Key Areas Covered

1. What is Apomixis
     – Definition, Features, Examples
2. What is Polyembryony
     – Definition, Features, Examples
3. What are the Similarities Between Apomixis and Polyembryony
     – Outline of Common Features
4. What is the Difference Between Apomixis and Apolyembryony
     – Comparison of Key Differences

Key Terms

Apomixis, Agamospermy, Asexual Reproduction, Fertilized Egg, Polyembryony, Sexual Reproduction

What is Apomixis

Apomixis is the replacement of normal sexual reproduction by asexual reproduction. It does not undergo fertilization or meiosis for the formation of gametes. In other words, it is the replacement of seeds from plantlets or bulbils. Therefore, the offspring is completely genetically-identical to the parent plant. Furthermore, apomixis is also known as agamospermy, which theoretically occurs in gymnosperms, producing clonal seeds. Additionally, in plants with independent gametophytes, this type of asexual reproduction is known as apogamy, which refers to the formation of sporophytes from the generative cells of the gametophyte by parthenogenesis.

Figure 1: Caribbean agave Producing Plantlets on the Old Flower Stem

However, in flowering plants, four types of apomixis can be identified; they are nonrecurrent apomixis, recurrent apomixis, adventive embryony, and vegetative apomixis. Here, nonrecurrent apomixis is the formation of a haploid embryo from the megaspore mother cell by undergoing mitosis. Recurrent apomixis is the presence of the same number of chromosomes in the mother plant of the megagametophyte due to incomplete meiosis. Also, adventive embryony is the arising of the embryos from the cells of the nucellus or the integument. On the other hand, vegetative apomixis is the replacement of flowers by bulbils.

What is Polyembryony

Polyembryony is the formation of two or more embryos from a single fertilized egg. Therefore, each embryo is genetically-identical to each other, but, none of them is genetically-identical to their parent. On that account, polyembryony is different from asexual reproduction such as budding or regular sexual reproduction. Interestingly, polyembryony occurs in humans as well but, in low frequency. Also, this results in identical twins.

Figure 2: Most Commercial Citrus Varieties Produce Mainly Nucellar Seedlings

In addition, it can occur in vertebrates, invertebrates, and plants. Armadillos are a well-known form of animals that undergo polyembryony. Also, Hymenoptera is an order of parasitic wasps that undergo polyembryony and it is an example of invertebrates that undergo polyembryony. However, in botany, polyembryony refers to the seedling arising from a single embryo. Here, the original embryo divides into identical embryos.

Similarities Between Apomixis and Polyembryony

• Apomixis and polyembryony are two methods of reproduction in plants.
• Both are responsible for the production of several genetically-identical individuals.
• Furthermore, they are alternative methods of reproduction for regular asexual or sexual reproduction.
• However, each embryo formed in both methods contains the same number of chromosomes as the parent.

Difference Between Apomixis and Polyembryony

Definition

Apomixis refers to an asexual reproduction that occurs without fertilization and not involving meiosis while polyembryony refers to the formation of more than one embryo from a single fertilized ovum or in a single seed. Thus, this is the main difference between apomixis and polyembryony.

Type of Reproduction

Also, another difference between apomixis and polyembryony is that apomixis is a type of asexual reproduction while polyembryony is a type of sexual reproduction.

Undergoing Fertilization

Furthermore, fertilization does not occur in apomixis while polyembryony undergoes fertilization. Hence, this is an important difference between apomixis and polyembryony.

Formation of Seeds

Moreover, apomixis is not involved in the production of seeds while polyembryony is involved in the production of seeds. Hence, this is also a difference between apomixis and polyembryony.

Genetic Identity to the Parent

The plants produced by apomixis are genetically-identical to the parent while the plants produced by polyembryony are not genetically-identical to the parent. Thus, this is one other difference between apomixis and polyembryony.

Conclusion

Apomixis is a type of asexual reproduction found in plants. It is responsible for the formation of embryos without undergoing fertilization. This means embryos develop from the generative tissues of the plant. In comparison, polyembryony is a type of sexual reproduction responsible for the formation of two or more embryos from a fertilized egg. It involves the formation of seeds as well. However, the main difference between apomixis and polyembryony is the process of reproduction.

References:

1. Bicknell, R. A. “Understanding Apomixis: Recent Advances and Remaining Conundrums.” The Plant Cell Online, vol. 16, no. suppl_1, 2004, doi:10.1105/tpc.017921.
2. “Polyembryony.” BYJU’S|The Learning App, Available Here.

Image Courtesy:

1. “Agave angustifolia (Caribbean Agave) in Hyderabad W IMG 8660” By J.M.Garg – Own work (CC BY 3.0) via Commons Wikimedia  
2. “Citrus fruits” By Scott Bauer, USDA – This image was released by the Agricultural Research Service, the research agency of the United States Department of Agriculture, with the ID K7226-29 (next). (Public Domain) via Commons Wikimedia