Final answer:
Reproductive isolation creates barriers to gene flow, which may arise from prezygotic or postzygotic barriers, preventing the exchange of genetic material between populations and leading to separate evolutionary pathways.
Step-by-step explanation:
True, reproductive isolation indeed leads to a barrier to gene flow. Reproductive isolation can occur through both prezygotic and postzygotic barriers. Prezygotic barriers, such as different breeding times (temporal isolation), incompatible reproductive parts, and differences in gamete cells, prevent fertilization from occurring. Postzygotic barriers, which occur after fertilization, might involve the creation of hybrid offspring that are infertile or less fit, thus preventing genes from being passed on to future generations. When either type of barrier is in place, the affected populations do not exchange genetic material, effectively leading to separate evolutionary pathways and potentially, over time, the emergence of new species.