Genetic Drift and Gene Flow

Genetics is a field of science that studies genes, how they are inherited, and the variation between living organisms.

Genes can be thought of as "instructions." When a living cell processes DNA (DeoxyriboNucleic Acid) the DNA is read as "codes" for what the cell needs to produce.

For example, one gene might instruct the cell to produce brown hair while another gene might instruct the cell to produce black hair. DNA consists of millions of little code sequences that instruct the cell to produce a wide assortment of different things. The result is the difference between you and every other living organism you see; you all have a different "code book."

The study of genetics involves all of the processes and mechanisms involved in the coding of genes, how they are inherited from one generation to the next, and how different genes result in different species.

Genetic drift is a genetic mechanism that affects evolution. Genetic drift is based on the idea that the percentages of genes in a population may change from one generation to the next based simply on chance, or just plain luck. Over time, these small changes from generation to generation ultimately may lead so significant changes over many years.

Unlike natural selection, or "survival of the fittest," genetic drift is not powered by the need to adapt to your surroundings. Genetic drift may in fact increase the ratio of a gene that isn't necessarily beneficial at all.

A simple example may be hair color in humans. Say, for example, a starting population has 33% of its people with blonde hair, 33% brown hair, and 33% have black hair. The next generation of people in that population may have (completely based on random chance) 27% blonde hair, 39% brown hair, and 34% black hair.

You see, the percentages of those genes changed from one generation to the next basely solely upon random chance.

Over many years, that population may eventually reach the point in which 90% of the people have brown hair, 7% have blonde, and only 3% have black hair.

In a nutshell, genetic drift changes the genetic makeup of a population due to random chance.

Its like flipping a coin. You may get "heads" 20% of the time and "tails" 80% of the time. However, during the next trial you may get 60% "heads" and then 40% "tails."

Its all about random chance and luck.

Gene flow, or genetic migration, is the process in which genes "flow" from one population to another. This movement of genes helps maintain genetic diversity, or genetic variation within populations.

If two populations were to be separated, then over time they may become more different from one another. Perhaps maybe one population may contain a specific gene that the other population does not contain. If an individual with that unique gene were to mate with an individual from the other population that didn't contain that gene, then gene flow would introduce that unique gene into that other population.

One of the best examples of gene flow is seen in the United States. The United States has been labeled as a "mixing pot" of all of the various nationalities around the world. For example, the genes of Australians make them unique, the genes of Italians make them unqiue, the genes of the British make them unique, and the genes of Russians make them unique. All of the different nationalities have some genes that make them a little bit different than all of the other nationalities.

However, with increased immigration to the United States, all of these different nationalities are coming together to form mixed genetics. This is gene flow! For example, going from 100% Italian to children that are 25% Italian, 25% Russian, 25% Australian, 15% British, and 10% Fench is a great example of gene flow. All of the genetic diversity is spreading within populations.

If two or more populations are separated, then over time they may become more and more different from one another due to the random chances of genetic drift. Or, if those two populations are in two very different locations then there is also the possibility for natural selection to further differentiate the populations.

Regardless of what the actual cause of differentiation is, gene flow will reduce the effects. Gene flow between populations will make those populations more similar to one another since they are "sharing" or "mixing" the gene pool.

So what is the relationship between genetic drift and gene flow?

Genetic drift makes populations more different, but then gene flow can make populations more similar. As a result, gene flow reduces the effects of genetic drift.

The genetic founder effect is the result of a new population being formed by a small portion of a larger population.

For example, the founder effect can be described by a small group of individuals moving to a new area and establishing a new population amongst themselves.

The best example would be an isolated island. Lets say you have a population of birds that either have green feathers, red feathers, or blue feathers. In the main population lets say that the genetic variation is evenly distributed as 1/3 green feathers, 1/3 blue feathers, and 1/3 red feathers. However, now lets say that only 5 of those birds fly off to that new and isolated island. These 5 birds are the "founders" of the new population.

Lets say out of those 5 birds, 4 of them were green birds and only 1 of them was a blue bird. Now the genetic diversity in this new population of birds on this isolated island is 80% green feathers, 20% blue feathers, and 0% red feathers. After this new population of birds begins reproducing, you may discover that their genetic variance results in 95% green birds and only 5% blue birds with 0 red birds.

You can see how different this new population is in comparison to the original population, and the mechanism is know as the founder effect. The genetic diversity of the founders of the new population will determine the ratio of genes in that population as it grows, and it will sometimes be much different than the original population due to the small sample size being taken out of a large pool and then being multiplied.