Reduced hybrid fertility is a barrier to speciation that occurs when

Question

BlackTom AI · Accepted Answer

Reduced hybrid fertility occurs when hybrid offspring are viable and appear healthy but cannot produce functional gametes and therefore cannot reproduce.

Relevant knowledge points: reproductive isolation can be prezygotic (preventing mating or fertilization) or postzygotic (after zygote forms). Postzygotic barriers include reduced hybrid viability (hybrids die or are weak), reduced hybrid fertility (hybrids survive but are sterile), and hybrid breakdown (fertility/fitness problems in later generations). Mechanisms include chromosomal mismatches, incompatible gene interactions (Dobzhansky–Muller incompatibilities), or problems in meiosis that prevent formation of balanced gametes.

Step-by-step reasoning:
1. Two distinct species mate and produce a zygote (so prezygotic barriers did not prevent mating).
2. The zygote develops into an apparently healthy individual — the hybrid is viable and robust.
3. During sexual maturation, problems arise in gametogenesis: meiosis fails to produce functional sperm or eggs, or gametes are inviable. These problems can stem from differing chromosome numbers/structures or incompatible alleles.
4. Because the hybrid cannot produce offspring, gene flow between the parent species is blocked, reinforcing reproductive isolation.

Why the correct answer is correct: The phrase “hybrid offspring are very robust but are sterile” exactly describes postzygotic reduced hybrid fertility — hybrids live and function but cannot reproduce, which prevents genetic exchange. Classic example: a mule (horse × donkey) is typically healthy and strong but usually sterile because horse and donkey chromosomes do not pair properly in meiosis.

Why other possibilities are incorrect: prezygotic barriers (mate choice, temporal isolation, mechanical isolation) prevent formation of hybrids, not fertility after hybridization. Reduced hybrid viability means hybrids die or are weak, not robust but sterile. Hybrid breakdown refers to fertile first-generation hybrids producing weak/sterile later generations, different from immediate sterility.

Therefore, the correct answer is: hybrid offspring are very robust but are sterile.

Reduced hybrid fertility is a barrier to speciation that occurs when单项选择题

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