Which mechanism can contribute to reproductive isolation without geographic separation?

Which mechanism can contribute to reproductive isolation without geographic separation?

• A. Polyploidy leading to instant reproductive isolation
• B. Migration of individuals to a new habitat several miles away
• C. A neutral mutation with no effect on mating
• D. Random mating within the same population

Answer: (A)

Polyploidy can create reproductive isolation without any geographic separation. When an individual ends up with a chromosome number that is a duplicate or otherwise different from the standard set, its gametes won’t pair properly with the normal chromosome complement during meiosis. As a result, offspring formed with the original diploid individuals are often sterile or inviable, while individuals with the same altered chromosome number can mate and produce fertile progeny among themselves. This creates a new, reproductively isolated lineage within the same geographic area—a process known as sympatric speciation. The other scenarios involve geographic separation or no effect on mating, so they don’t produce isolation within a single location. Migration to a new habitat introduces physical barriers; a neutral mutation that doesn’t affect mating won’t prevent interbreeding; random mating within the same population maintains gene flow.

Polyploidy can create reproductive isolation without any geographic separation. When an individual ends up with a chromosome number that is a duplicate or otherwise different from the standard set, its gametes won’t pair properly with the normal chromosome complement during meiosis. As a result, offspring formed with the original diploid individuals are often sterile or inviable, while individuals with the same altered chromosome number can mate and produce fertile progeny among themselves. This creates a new, reproductively isolated lineage within the same geographic area—a process known as sympatric speciation.

The other scenarios involve geographic separation or no effect on mating, so they don’t produce isolation within a single location. Migration to a new habitat introduces physical barriers; a neutral mutation that doesn’t affect mating won’t prevent interbreeding; random mating within the same population maintains gene flow.