In multiple freshwater populations showing plate loss, what genetic pattern would most strongly indicate parallel evolution?

• A. Completely different genes in each population.
• B. Plate loss occurs without any genetic change.
• C. Shared genetic changes in the same genomic regions across populations.
• D. Plate loss occurs only in one population.

Answer: (C)

Parallel evolution occurs when independent populations adapt to similar environments by using the same genetic changes. In freshwater sticklebacks, plate loss repeatedly happens as an adaptive response to freshwater conditions. If multiple freshwater populations show plate loss and the same genomic regions carry changes in each population, that pattern strongly indicates they’re using the same genetic route to reach the same trait. This shared genetic signal across populations points to parallel evolution, driven by similar selective pressures selecting for the same genetic solutions.

If different genes were involved in each population, it would suggest convergent evolution rather than parallel. Plate loss without any genetic change would imply a non-genetic cause, and plate loss restricted to a single population wouldn’t demonstrate parallel evolution across populations.