Difference Between Prezygotic and Postzygotic

The key difference between prezygotic and postzygotic is that the prezygotic is a mechanism of reproductive isolation, which prevents the fertilization of the egg while the postzygotic is a mechanism of reproductive isolation, which prevents the formation of viable or fertile offspring.

A species is a group of organisms that can sexually reproduce with one another in nature and produce fertile offspring. In the evolutionary aspect, speciation is an important concept. Species is a reproductively isolated group. Prezygotic and postzygotic are two main reproductive isolation mechanisms. The reproductive isolation that occurs before fertilization is the prezygotic isolation. While, the reproductive isolation that occurs after fertilization and prevents the fertilized egg to become a fertile offspring is the post-zygotic isolation.

CONTENTS

1. Overview and Key Difference
2. What is Reproductive Isolation
3. What is Prezygotic Isolation
4. What is Postzygotic Isolation
5. Similarities Between Prezygotic and Postzygotic
6. Side by Side Comparison – Prezygotic vs Postzygotic in Tabular Form
7. Summary

What is Reproductive Isolation?

Reproductive isolation refers to a set of mechanisms that prevent species or the members of the same group from breeding or mating with each other. Thus, it prevents the production of fertile offspring. Several mechanisms are responsible for reproductive isolation. Among them, prezygotic and postzygotic are two main mechanisms.

What is Prezygotic Isolation?

Prezygotic reproductive isolation is a mechanism of reproductive isolation that prevents the fertilization of the eggs. There are different categories of prezygotic isolation mechanism. They are behavioural isolation, habitat isolation, mating seasons, mechanical isolation, temporal isolation, gamete isolation, etc. When the two species live in a completely different two habitats where they cannot meet with each other, it prevents the fertilization, and it is known as habitat isolation.

Furthermore, when the mating seasons differ among the species, they don’t prefer to mate with each other, and it will also prevent the union of sperms and eggs. Individuals may not mechanically fit with each other, or their gametes can be incompatible on some occasions. Both these reasons also can prevent the fertilization. Behavioural isolation occurs when the species are not aware of the mating rituals or when there is no sexual attraction, etc.

What is Postzygotic Isolation?

Postzygotic is another mechanism of reproductive isolation that prevents the formation of viable or fertile offspring even though the fertilization is completed. Hybrid inviability, hybrid breakdown, hybrid sterility are the major reasons for postzygotic isolation. The zygote which produced by the fertilization can be incapable of sustaining its life.

Furthermore, the produced zygote may not be mature enough to produce an offspring (immature zygote). Though the zygote matures into an adult, that adult may possess very low fertility level, hence incapable of giving birth to an offspring. All these factors can be responsible for the postzygotic isolation and prevention of the producing a fertile offspring.

What are the Similarities Between Prezygotic and Postzygotic Isolation?

• Prezygotic isolation and postzygotic isolation are two mechanisms of reproductive isolation.
• Both prevent the production of fertile offspring.
• They are important evolutionary processses.

What is the Difference Between Prezygotic and Postzygotic?

Prezygotic and postzygotic are two mechanisms of reproductive isolation. Prezygotic isolation prevents the fertilization of the egg while postzygotic isolation prevents the formation of a fertile offspring. Both mechanisms ultimately block the mating and production of a fertile offspring.

The below infographic presents the difference between prezygotic and postzygotic isolation in tabular form.

Summary – Prezygotic vs Postzygotic

The inability of the members of species to mate and produce fertile offspring is the phenomenon called reproductive isolation. There are a set of mechanisms responsible for this. Prezygotic and postzygotic are two mechanisms. Prezygotic isolation prevents the union of sperms and eggs whereas postzygotic isolation prevents the formation of a fertile offspring even after the fertilization. This is the difference between prezygotic and postzygotic isolation.

Reference:

1.“Reproductive Isolation – Prezygotic – Postzygotic – Biology Video by Brightstorm.” Brightstorm. Available here
2.“A Brief Explanation of Reproductive Isolation With Examples.” BiologyWise, BiologyWise, 14 July 2017. Available here

Image Courtesy:

1.”Sympatric Speciation with examples of all 3 types”By Nathaly Tamayo – Own work, (CC BY-SA 4.0) via Commons Wikimedia