Although they both prevent successful interbreeding among members of different species,
isolating mechanisms prevent the formation of a zygote, whereas
isolating mechanisms prevent successful reproduction of a hybrid after successful fertilization has occurred.

Question

Although they both prevent successful interbreeding among members of different species, 
 isolating mechanisms prevent the formation of a zygote, whereas 
 isolating mechanisms prevent successful reproduction of a hybrid after successful fertilization has occurred.

BlackTom AI · Accepted Answer

The question presents a two-blank statement about isolating mechanisms and asks you to fill in the appropriate terms for each blank.

First blank (空白1): What type of isolating mechanism prevents the formation of a zygote? Prezygotic barriers act before fertilization and stop mating or fertilization from occurring, so they prevent a zygote from forming. Examples include temporal isolation (mating at different times), habitat isolation (different environments), behavioral isolation (different courtship), mechanical isolation (incompatible reproductive structures), and gametic isolation (gametes can’t fuse). Therefore, the correct fill for the first blank is prezygotic.

Second blank (空白2): What type of isolating mechanism prevents the successful reproduction of a hybrid after fertilization has occurred? Postzygotic barriers operate after fertilization, reducing the fitness of hybrids or preventing them from reproducing. Classic examples are reduced hybrid viability (hybrids die before reproducing), reduced hybrid fertility (hybrids are sterile, e.g., mules), and hybrid breakdown (hybrids are healthy at first but sterile or inviable in later generations). Hence, the correct fill for the second blank is postzygotic.

In summary, when describing barriers to reproductive isolation:
- Prezygotic barriers prevent zygote formation
- Postzygotic barriers prevent successful reproduction after fertilization
The two blanks should be filled as: prezygotic for the first, postzygotic for the second.

Although they both prevent successful interbreeding among members of different species, isolating mechanisms prevent the formation of a zygote, whereas isolating mechanisms prevent successful reproduction of a hybrid after successful fertilization has occurred.

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