Gene flow describes the transfer of genetic material from one population of a species to another. This movement often occurs when individuals or their reproductive cells migrate and successfully reproduce in a new location. Like mixing two different colors of paint, this process introduces new genetic variations into populations, making them more similar to each other.
Animal Migration and Gene Flow
Physical movement of individuals is a straightforward way for genes to spread across landscapes. Consider the gray wolf (Canis lupus), known for its wide-ranging movements across North America and Eurasia. A young wolf might travel many miles to find a new territory or mate. When this individual successfully breeds with wolves from a different pack, it introduces its unique genetic variants into that new population’s gene pool.
This movement prevents isolated wolf packs from becoming too genetically distinct. For example, a male wolf dispersing from a pack in Yellowstone National Park might join a pack in an adjacent forest. His offspring in the new pack will carry genes originating from his birth pack. This ongoing exchange helps maintain genetic diversity across the broader wolf population.
Pollen and Seed Dispersal in Plants
Gene flow in plants often occurs without the entire organism physically relocating. Pollen, which contains the male genetic material, can travel considerable distances. Wind, for instance, can carry pine pollen from one stand of trees to another, facilitating gene exchange. Similarly, insects like bees can transport pollen grains as they forage between wildflowers in different meadows.
Beyond pollen, seeds also play a significant role in plant gene dispersal. A bird consuming berries from one plant may later excrete the seeds far away, allowing a new plant to grow and potentially introduce its genes into a distant population. This mechanism ensures that even sessile plants can contribute to the genetic mixing of their species across broad areas.
Consequences of Obstructed Gene Flow
When gene flow is interrupted, populations can begin to diverge genetically. Barriers, which can be natural or human-made, prevent the movement of individuals or genetic material between groups. A mountain range or a large river serves as a natural barrier, while human constructions like major highways or dams act as artificial obstructions.
For example, a busy highway can effectively divide a previously continuous population of squirrels. Squirrels on one side may be unable to cross the road to interact and breed with those on the other side. Over many generations, without the interbreeding that gene flow provides, these two isolated squirrel populations will accumulate different genetic changes due to random mutations and natural selection. This genetic isolation is a fundamental step in the process that can eventually lead to the formation of new, distinct species.