How does geographic isolation cause an increase in differences between two groups

What was once a continuous population is divided into two or more smaller populations. This can occur when rivers change course, mountains rise, continents drift, or organisms migrate. The geographic barrier isn't necessarily a physical barrier that separates two or more groups of organisms. It might just be unfavorable habitat between the two populations that keeps them from mating with one another.

Explanation:

the correct answer is: b. pantala flavescens, because these organisms would have a high level of genetic variation due to sexual reproduction.  

because involves two organisms (parents) whose genetic material combines, sexual reproduction leads to genetic variation in new generations of offspring. the offspring is an unique organism, with new genome, more protected with the higher ability to adapted. this process is fundamental to evolution.

answer: dna

because all cells have genes