Gene flow, the transfer of genetic material between populations, can have significant effects on genetic variation. Here's how it impacts genetic variation based on your options:
- a. has no effect on genetic variation: This is incorrect because gene flow does affect genetic variation.
- b. increases genetic variation between populations: This option is also incorrect because gene flow tends to homogenize genetic variation between populations rather than increase it.
- c. reduces genetic variation within a population: This can be somewhat true, but it is not the primary effect since gene flow usually introduces new alleles into a population.
- d. increases genetic variation within a population: This is the correct choice. Gene flow generally introduces new alleles into a population, which can increase genetic variation within that population.
Thus, the best answer is d. increases genetic variation within a population.