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Chapter 24 Section 4: Genetic Drift (Siddarth)

Page history last edited by Siddarth Santhebennur 13 years, 2 months ago

A. Chapter Summary 

     Welcome! I am sure you are all excited to read about Genetic Drift! So what exactly is Genetic Drift? It is when your genes decide to drift from place to another. JUST KIDDING! Genetic drift is pretty much a random change that occurs in a population's allele frequency from generation to the next and will end up changing the allele that is expressed. Genetic Drift favors either the elimination or continuation of an allele in a population. This ends up giving a population a frequency of 100% or 0%. Now if you were to look at my section, you would notice that they mention that Genetic Drift works better in a small population. Why is this? Think about flipping a coin. The number of times you flip a coin is considered to be your population. Let the head's and tail's side represent alleles that could possibly be expressed. If you were to have a very large population, you may have an equal frequency between head's & tail's because you are constantly flipping the coin. It's a 50-50 shot! Whereas a small population, you only have a few members in a population and have only flipped the coin a few times. By chance, you may receive results where they are more prominent and will stand out after a few flips. This is a pretty basic explanation of what occurs between large and small populations BUT there is an image I will  provide which shows an example between mice and the color of their fur. Genetic Drift has two categories: The Bottleneck Effect & The Founder Effect.

     The bottleneck effect is when a population suddenly decreases, but then grows back to its original size. The reason this is falls under the category of Genetic Drift is because there possibly could have been some allele loss. Since the population decreases, Genetic Drift reduces the variation between alleles. Genetic Drift ALWAYS results in the reduction of genetic variation. As mentioned above, this is a randome event that focuses on either the elimination or continuation of an allele being expressed within a population. An example of this can be seen in Figure #2 which shows a small population of bugs. This small population consists of various colors, but some of them die because the evil human being decided to walk right across them. Now since there was a small population to begin with, those colored bugs may not exist in the future population due to its extermination. The founder effect is when a minute group of organisms decide to migrate from the original population and prosper in a new area. The new population is expected have a reduce in genetic variation because of the fact that there are only a few individuals within in the group. There is a possibility that the allele frequencies in the new population differ from the original population which leads to certain alleles being expressed/not expressed.

     I will explain a great example of the founder effect in my virtual lecture which YOU ALL SHOULD WATCH! Now we have a rebellious scientist who courageously shut down Darwin's idea of Natural Selection...well not completely. An Evolutionary Biologist by the name of Motoo Kimura had the idea that genetic drift was the cause of a change in genetic variation rather than natural selection. He thought that genetic drift promoted neutral variation. For those of you who don't know (I am assuming all of you folks), Neutral Variation is a form of genetic drift that does not favor any genotype and does not affect reproductive success. Kimura formed a theory known as: The Neutral Theory of Evolution. This theory stated that genetic variation is primarily due to the combination of multiple neutral mutations that have become very popular (or have a high frequency) amongst a population through the process of Genetic Drift. Neutral Mutations don't play a major role in changing gene expression. All this does is change an amino acid in a codon which doesn't really effect the translation. Our man Kimura also coined the term non-Darwinian evolution. Non-Darwinian Evolution is the idea that that any genetic variation that occurs is due to the change in gene sequences. This is due to neutral variation as compared to Natural Selection's: Adaptive Variation. Kimura did agree that there are certain changes that occur due to Natural Selection such as adaptive changes. However he believed that any variation in DNA can be explained by neutral variation. 

B. Useful Materials


This is a great video which explains what I have summarized in the Chapter Summary above. For those of you who are visual learners this will help a lot! It helped me when I was trying to explain certain points in my Prezi. It mainly gives a general idea of what Genetic Drift is and the different kinds that have been observed: Bottleneck Effect & Founder Effect. 



Amazing...this video will blow your mind. It is worth every minute! Trust me! For those of you who would like to have a better understand of what Neutral Mutations do in the case of Genetic Drift this is a great video to watch. It may seem dragging, but I found it very interesting.  




Genetic Drift Simulations 
This is a great site that is pretty much a simulation of Genetic Drift. This site allows you to create your own scenarios and see what kind of effects happen due to the changes you may have made to the population or the environment. 



Founder effect and estimation of the age of the French Gypsy mutation associated with Glanzmann thrombasthenia in Manouche families

I had to bring in an article from pubMed! This is a great article which shows an investigation of a substitution of a certain nucleotide that has caused a mutation in Manouche Families. Scientists are tracing the roots back and claim that this could possibly the work of the Founder Effect.  


C. Virtual Lecture

D. Prezi



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