Gene Flow: Videos & Practice Problems

Gene flow is the movement of individuals or gametes between populations with different allele frequencies, impacting allele frequencies and promoting evolution. This process generally reduces genetic variation between populations, making them more similar. It can introduce new alleles or reintroduce lost alleles, enhancing genetic diversity. For example, in butterfly populations separated by a river, gene flow can lead to increased similarity as individuals migrate and share alleles, illustrating the significance of gene flow in evolutionary mechanisms.

Gene Flow

Gene flow is a crucial mechanism in the process of evolution, defined as the movement of individuals or gametes between populations that possess different allele frequencies. When individuals migrate from one population to another, they carry their alleles with them, which can significantly alter the allele frequencies in both populations. This movement generally leads to a reduction in genetic variation between the two populations, making them more similar over time.

For instance, consider two populations of butterflies separated by a river. Initially, these populations exhibit distinct allele frequencies. However, as individuals move between these populations, they introduce new alleles or reintroduce alleles that may have been lost due to genetic drift or other factors. This process not only enhances genetic diversity within a population but also contributes to the homogenization of allele frequencies across populations.

In summary, gene flow plays a vital role in shaping the genetic landscape of populations by reducing differences in allele frequencies and potentially introducing new genetic material. This dynamic process is essential for understanding how populations evolve and adapt over time, as it influences genetic variation and the overall evolutionary trajectory of species.

Gene Flow Example 1

Isle Royale, located in Lake Superior off the coast of Michigan's Upper Peninsula, is a significant site for ecological studies, particularly concerning the interactions between wolf and moose populations. The island's wolf population fluctuates between approximately 10 to 50 individuals, which is notably small and makes it an ideal case for observing evolutionary mechanisms.

One key concept to understand in this context is genetic drift, which is the change in the frequency of a gene variant (allele) in a population due to random sampling. In small populations like that of the wolves on Isle Royale, genetic drift occurs more rapidly because random events can have a larger impact on the overall genetic makeup of the population. This can lead to a loss of genetic diversity over time.

Another important factor is inbreeding depression, which occurs when closely related individuals breed, resulting in a higher likelihood of homozygosity for deleterious alleles. This can decrease the overall fitness of the population, as harmful recessive traits become more prevalent. The wolves on Isle Royale, being closely related due to their small population size, are particularly susceptible to this phenomenon.

The formation of ice bridges during cold winters allows for the movement of wolves and other animals between the island and the mainland, facilitating gene flow. Gene flow is the transfer of genetic material between populations, which can introduce new alleles and increase genetic diversity. This process can counteract the effects of genetic drift and inbreeding depression by providing new genetic material that enhances the overall fitness of the population.

If ice bridges no longer form due to climate change, maintaining the genetic health of the wolf population becomes challenging. A potential solution would be to import wolves from the mainland periodically. This action would reintroduce genetic diversity, helping to mitigate the effects of genetic drift and inbreeding depression. By increasing the gene pool, the fitness of the wolf population on Isle Royale could be preserved, allowing it to sustain itself over time despite the challenges posed by its isolated environment.

To boost wild populations of fish such as Atlantic Salmon, scientists will sometimes breed fish in captivity and then release the fish into the wild population. Below, scientists measured the fitness of the wild fish, the captive-bred fish after being released into the wild population, and the first-generation offspring of wild and captive-bred fish. The fitness values are reported as relative values between 0 and 1. What description below best explains the data?

• A. The first-generation offspring of wild and captive-bred fish are likely less fit due to inbreeding depression.
• B. Gene flow into the wild population from the captive population has increased genetic variation in the wild fish; therefore, wild-caught fish now have the highest fitness.
• C. Wild populations likely have the highest population size and, therefore, are less subject to genetic drift, meaning they will have the highest fitness.
• D. Captive-bred fish are poorly adapted to living in the wild, and gene flow from captive populations into wild populations can be expected to reduce the overall fitness of the wild population.

Answer: (D)

Here’s what students ask on this topic:

What is gene flow and how does it affect allele frequencies in populations?

Gene flow is the movement of individuals or gametes between populations with different allele frequencies. This process can significantly impact allele frequencies within those populations. When individuals migrate, they bring their alleles with them, which can introduce new alleles or reintroduce alleles that may have been lost due to genetic drift or other mechanisms. As a result, gene flow generally reduces genetic variation between populations, making them more similar to each other. This movement of alleles can promote evolution by increasing genetic diversity and enabling populations to adapt to changing environments.

How does gene flow contribute to evolution?

Gene flow contributes to evolution by altering allele frequencies within populations. When individuals or gametes move between populations, they bring new genetic material, which can introduce new alleles or reintroduce lost alleles. This exchange of genetic material increases genetic diversity within populations, providing a broader range of traits for natural selection to act upon. Over time, gene flow can lead to populations becoming more similar to each other, reducing genetic variation between them. This process is essential for the adaptation and survival of populations in changing environments, ultimately driving evolutionary change.

Can gene flow introduce new alleles to a population? If so, how?

Yes, gene flow can introduce new alleles to a population. When individuals from one population migrate to another, they bring their genetic material with them. If these individuals carry alleles that are not present in the recipient population, those alleles can be introduced into the gene pool. This introduction of new alleles can increase genetic diversity within the population, providing new traits that may be beneficial for survival and reproduction. Over time, these new alleles can become more common in the population through natural selection, contributing to evolutionary change.

What is the impact of gene flow on genetic variation between populations?

Gene flow generally reduces genetic variation between populations. When individuals or gametes move between populations, they bring their alleles with them, which can lead to the exchange of genetic material. This exchange makes the allele frequencies in the populations more similar to each other, decreasing the genetic differences between them. As a result, populations that experience gene flow tend to become more genetically homogeneous over time. This reduction in genetic variation between populations can have significant implications for their ability to adapt to different environments and may influence the overall evolutionary trajectory of the species.

How does gene flow differ from genetic drift?

Gene flow and genetic drift are both mechanisms of evolution, but they operate differently. Gene flow involves the movement of individuals or gametes between populations, leading to the exchange of genetic material and altering allele frequencies. This process generally reduces genetic variation between populations and increases genetic diversity within populations. In contrast, genetic drift is a random process that causes changes in allele frequencies due to chance events, such as natural disasters or random sampling of alleles during reproduction. Genetic drift can lead to the loss of alleles and reduced genetic diversity within populations, and it tends to have a more significant impact in small populations.