Which postzygotic barrier occurs when the first generation hybrids are fertile, but later generations are weak or sterile?

Which postzygotic barrier occurs when the first generation hybrids are fertile, but later generations are weak or sterile?

• A. Hybrid inviability
• B. Hybrid sterility
• C. Hybrid vigor
• D. Hybrid breakdown

Answer: (D)

The main idea is how some postzygotic barriers only show up after several generations due to genetic incompatibilities between the parental genomes. In this scenario, the first generation hybrids are viable and fertile because having one copy of each parental genome masks harmful interactions. But when these hybrids breed or produce backcrosses, new allele combinations can reveal incompatible interactions, leading to reduced viability or sterility in the offspring of later generations. This pattern is called hybrid breakdown. The other possibilities don’t fit this pattern: hybrid inviability would cause hybrids to die before reaching reproductive age; hybrid sterility would make the first-generation hybrids sterile; hybrid vigor (heterosis) describes increased fitness in hybrids, not a generation-limited breakdown.

The main idea is how some postzygotic barriers only show up after several generations due to genetic incompatibilities between the parental genomes. In this scenario, the first generation hybrids are viable and fertile because having one copy of each parental genome masks harmful interactions. But when these hybrids breed or produce backcrosses, new allele combinations can reveal incompatible interactions, leading to reduced viability or sterility in the offspring of later generations. This pattern is called hybrid breakdown.

The other possibilities don’t fit this pattern: hybrid inviability would cause hybrids to die before reaching reproductive age; hybrid sterility would make the first-generation hybrids sterile; hybrid vigor (heterosis) describes increased fitness in hybrids, not a generation-limited breakdown.