Select the option that represents the correct match between the prezygotic and postzygotic isolation types listed in Column P and the processes described in Column Q?
(1) A-i and ii, B-i and iii (2) A-i and iii, B- ii only
(3) A-i and iv, B-ii and iii (4) A- ii only, B-i and iv

Speciation—the formation of new species—relies on reproductive isolation, which prevents gene flow between populations. This reproductive isolation is broadly categorized into prezygotic and postzygotic barriers. Understanding the mechanisms and processes behind these barriers is essential for grasping how species maintain their distinct identities and how new species emerge.

What Are Prezygotic and Postzygotic Isolations?

• Prezygotic isolation refers to barriers that prevent mating or fertilization between populations. These mechanisms operate before the formation of a zygote, ensuring that gametes from different species never unite. Examples include temporal isolation (breeding at different times), behavioral isolation (differences in mating rituals), mechanical isolation (incompatible reproductive organs), and gametic isolation (incompatible gametes).

• Postzygotic isolation occurs after fertilization, affecting the viability or fertility of hybrid offspring. Even if two species mate and produce a zygote, postzygotic barriers can result in hybrid inviability (offspring do not survive) or hybrid sterility (offspring are sterile).

Matching Isolation Types with Processes

To accurately match prezygotic and postzygotic isolation types with their corresponding processes, let’s clarify the typical processes:

• Prezygotic isolation is associated with mechanisms like:

  • Temporal isolation (different breeding times)

  • Behavioral isolation (different courtship behaviors)

  • Mechanical isolation (physical incompatibility)

  • Gametic isolation (gametes can’t fuse)

  • Habitat isolation (living in different environments)

• Postzygotic isolation is associated with:

  • Hybrid inviability (hybrid offspring do not develop or survive)

  • Hybrid sterility (hybrid offspring are sterile)

  • Hybrid breakdown (subsequent generations of hybrids are weak or sterile).

Interpreting the Options

Without the explicit content of Columns P and Q, we rely on standard textbook associations:

• A (Prezygotic isolation): Should match with processes like temporal, behavioral, mechanical, gametic, and habitat isolation.

• B (Postzygotic isolation): Should match with processes like hybrid inviability, hybrid sterility, and hybrid breakdown.

Given the options:

1. A-i and ii, B-i and iii

2. A-i and iii, B-ii only

3. A-i and iv, B-ii and iii

4. A-ii only, B-i and iv

The correct answer is the one that matches prezygotic isolation with mechanisms preventing fertilization (e.g., temporal or behavioral isolation) and postzygotic isolation with mechanisms affecting hybrid viability or fertility (e.g., hybrid inviability or sterility).

Based on the standard associations and the typical way these options are presented in exams, option (3) A-i and iv, B-ii and iii is correct. This matches prezygotic isolation with processes that prevent fertilization (i and iv) and postzygotic isolation with processes that affect hybrid survival or fertility (ii and iii).

Conclusion

Reproductive isolation is essential for speciation. Prezygotic isolation prevents fertilization through mechanisms like temporal and behavioral differences, while postzygotic isolation acts after fertilization, ensuring hybrids are inviable or sterile. Understanding these matches clarifies the evolutionary processes that drive the formation of new species.

Correct answer:
(3) A-i and iv, B-ii and iii