Pre-zygotic and post-zygotic isolation are mechanisms of reproductive isolation that prevent species from interbreeding and producing fertile offspring. Here's a breakdown of each:
Pre-zygotic Isolation:
Pre-zygotic isolation mechanisms occur before fertilization, preventing the formation of a zygote. These mechanisms include:
1. Temporal Isolation: Species breed at different times of the day, season, or year.
2. Habitat Isolation: Species live in different habitats and do not meet.
3. Behavioral Isolation: Species have different mating rituals or behaviors.
4. Mechanical Isolation: Differences in reproductive anatomy prevent successful mating.
5. Gametic Isolation: Sperm and egg are incompatible, preventing fertilization.
Post-zygotic Isolation:
Post-zygotic isolation mechanisms occur after fertilization, affecting the viability or fertility of the hybrid offspring. These mechanisms include:
1. Hybrid Inviability: Hybrid offspring do not develop properly and die early.
2. Hybrid Sterility: Hybrid offspring are sterile and cannot reproduce (e.g., mules, which are hybrids of horses and donkeys).
3. Hybrid Breakdown: Hybrid offspring are fertile, but their descendants are inviable or sterile.
These mechanisms help maintain species boundaries and prevent gene flow between different species.
Correct option: Pre-zygotic isolation mechanisms occur before fertilization, while post-zygotic isolation mechanisms occur after fertilization.