Which reproductive isolation mechanism occurs before zygote formation?

Which reproductive isolation mechanism occurs before zygote formation?

• A. Prezygotic Barrier
• B. Postzygotic Barrier
• C. Ecological Isolation
• D. Intrasexual Selection

Answer: (A)

Barriers that act before fertilization prevent a zygote from forming. These are prezygotic barriers, because they stop mating or fertilization itself. Examples include differences in mating times, habitats, proper courtship signals, mechanical incompatibilities, or gamete incompatibility. Since fertilization never occurs, the zygote is not produced. In contrast, postzygotic barriers operate after a zygote forms, reducing hybrid viability or fertility. Ecological isolation fits under prezygotic barriers (habitat differences prevent encounters), while intrasexual selection is about mate competition within a sex and isn’t a reproductive isolation mechanism between species.

Barriers that act before fertilization prevent a zygote from forming. These are prezygotic barriers, because they stop mating or fertilization itself. Examples include differences in mating times, habitats, proper courtship signals, mechanical incompatibilities, or gamete incompatibility. Since fertilization never occurs, the zygote is not produced. In contrast, postzygotic barriers operate after a zygote forms, reducing hybrid viability or fertility. Ecological isolation fits under prezygotic barriers (habitat differences prevent encounters), while intrasexual selection is about mate competition within a sex and isn’t a reproductive isolation mechanism between species.