![]() ![]() As a result, the population expresses unusually high incidences of Huntington’s disease (HD) and Fanconi anemia (FA), a genetic disorder known to cause bone marrow and congenital abnormalities, and even cancer. This is likely due to a higher-than-normal proportion of the founding colonists, which were a small sample of the original population, carried these mutations. The founder effect is believed to have been a key factor in the genetic history of the Afrikaner population of Dutch settlers in South Africa, as evidenced by mutations that are common in Afrikaners but rare in most other populations. The founder effect occurs when the genetic structure matches that of the new population’s founding fathers and mothers. In this situation, those individuals are unlikely to be representative of the entire population which results in the founder effect. See below for some links to actual human examples of natural selection and genetic drift (gene flow is pretty self-explanatory).\): A chance event or catastrophe can reduce the genetic variability within a population.Īnother scenario in which populations might experience a strong influence of genetic drift is if some portion of the population leaves to start a new population in a new location, or if a population gets divided by a physical barrier of some kind. And there are plenty of examples of each out there in the world. Genetic drift occurs in all populations of non-infinite size, but its effects are strongest in small populations. The percentage of certain versions of genes can change because new versions move in, certain versions are lost or gained by accident, or certain genes do better in a certain environment. Key points Genetic drift is a mechanism of evolution in which allele frequencies of a population change over generations due to chance (sampling error). (Image from Wikimedia)Īnd that's all there is to these concepts. Natural selection or genetic drift? Scientists still aren't sure when it comes to eye color. The frequency of brown eye alleles has increased in the population because of natural selection. We are back to having more brown eye alleles in the population. Over time, there will be an increase in the number of brown eye alleles in the population because everyone with blue alleles dies out or at least doesn't do as well. Whatever the reason, the Swedes have fewer kids in general than do the native Rwandans. Or their associated fair skin leads to lots of birth defects and skin cancer because sunscreen and/or vitamin B supplements haven't been invented yet. Maybe these folks are blinded by the sun and so tend to get eaten by lions. This is genetic drift - the percentage of blue eye alleles has decreased in the population because of a random event.įinally, let's say that for some reason blue eyes are a real disadvantage in Africa. The village has now returned to having mostly brown versions of the eye color gene. A freak storm comes and kills all of them. Now imagine that all the Swedes live in the north part of the village. Gene flow can increase genetic variation by introducing new alleles into a population or maintain existing variation. The gene frequency of the blue allele has increased in this population because of gene flow. The blue eye version (or allele) of an eye color gene has flowed into the population.īefore the population had 100% brown versions. This sudden influx of genes that lead to blue eyes being present in the village is gene flow. The Rwandans all have brown eyes and almost no one even has blue eyes hidden in their genes. Imagine a group of blue-eyed Swedes up and moves to a small village in Rwanda. ![]() As I like to do, I'll focus on eye color. I think the easiest way to understand them is to use an example. Otherwise they'd take forever to discuss anything even remotely complicated.īut these terms do take some explaining for the rest of us. ![]() They need this kind of shorthand to talk to each other about these ideas. These really are simple ideas wrapped in complicated terms. Scientists can make things so hard with their jargon. ![]()
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