What is Gene Flow?

Also called Gene Migration, gene flow is the phenomenon where genetic material is introduced from one population of a species to another through interbreeding. This essentially changes the gene pool of the recipient population – making new combinations of traits possible. However, it is important to note that it does not change the frequencies of alleles of a species as a whole. It does tend to change the allele frequencies of local populations. For instance, this phenomenon is observed in human populations that migrate from one region (continent) to another.

Speciation and its Barriers

Sometimes, there are certain factors that inhibit the ability to exchange genetic material between populations. In biology, these barriers can be classified into the following categories:

  • Allopatric Speciation
  • Sympatric Speciation
  • Parapatric Speciation
  • Artificial Speciation

Allopatric Speciation

If gene flow is blocked due to a physical barrier, then this phenomenon is called Allopatric speciation. For instance, physical barriers can range from natural barriers (such as geographic isolation) to man made barriers (such as China’s Great Wall). Geographic isolation may exist if a population is stranded on an island which is hundreds of kilometers away from the mainland. It can also include vast deserts, impassable mountains and deep canyons.

Sympatric Speciation

When gene flow is not blocked due to a physical barrier, it is termed as sympatric speciation. Such scenarios usually present a reproductive barrier, where certain incompatibilities can affect the ability to reproduce between populations of a species. However, this is a controversial subject as some biologists do not believe that this phenomenon exists. Regardless, there are examples of this phenomenon that support this theory. For example, the apple maggot is an insect that lays its eggs inside apples – and this eventually causes it to rot and drop to the ground. Once the fruit drops, the maggot burrows into the ground and then emerges as an adult fly after a few months. However, the apple maggot originally laid its eggs in another fruit called Hawthorn, which is related to apples. Since this does not make them unrelated to each other, biologists believe that this is an example of sympatric speciation.

Peripatric Speciation

This type of barrier arises when a small group of individuals break off from a much larger group and form a completely new species. This is quite similar to allopatric speciation where the populations are prevented from exchanging genes due to physical barriers. The primary characteristic of this type of speciation is that one of the populations is smaller than the other. Biologists have also pointed out that it can be quite difficult to distinguish between the two populations.

Artificial Speciation

As the name suggests, artificial speciation is done by humans, where we create new species. This is most done through experimentation. The most common example of this type of speciation is the fruit flies, which are specially bred for lab experiments.

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