Genetic Drift Founders and Bottleneck
My AP Biology Thoughts
Episode #11
Welcome to My AP Biology Thoughts podcast, my name is Pauline and I am your host for episode #11 called Unit 7 Evolution: Genetic Drift Founders and Bottleneck. Today we will be discussing one of the four evolutionary forces called genetic drift and its two examples.
Segment 1: Introduction to Genetic Drift Founders and Bottleneck
- There are 4 evolutionary forces that drive changes in a population’s genetics; these include natural selection, sexual selection, genetic drift, and gene flow
- The Founders and bottleneck effect fall under the evolutionary force of genetic drift
- Genetic drift consists of random non-adaptive changes due to a random event
- The Founders effect takes place when members of a population migrate to a new area. The founder’s effect is usually a catalyst to adaptive radiation which is an evolutionarily rapid change between populations
- The bottleneck effect occurs when a population experiences a catastrophic event (due to natural disaster, overharvesting, or habitat loss) that results in the survival of only a small number of individuals, who represent only a fraction of the genetic diversity that was present in the original population.
Segment 2: Example of Genetic Drift Founders and Bottleneck
- Founders effect: This is exemplified by the Eastern Pennsylvania Amish population. Their ancestors migrated from Germany to found their community. The Amish typically marry from within their own community and are isolated, so genetic mutations tend to persist. For this reason, the Ellis-van Creveld syndrome is much more prevalent among their population. The main symptoms of this disorder is short stature and abnormal numbers of fingers and toes.
- Bottleneck effect: A common example of this involves the Northern elephant seals. Humans inflicted upon them a population bottleneck through seal hunting. Hunters harvested the Northern elephant seal for its blubber to make oil. The blubber of one adult male elephant seal could produce up to 25 gallons of oil. By the late 1880’s, the seals were considered functionally extinct due to excessive harvesting. The effective breeding population reached a low point of 20-100 individuals. These survivors were moved to Guadalupe island to recover.
https://www.thoughtco.com/what-is-the-founder-effect-4586652
https://www.fisheries.noaa.gov/species/northern-elephant-seal
Segment 3: Digging Deeper
How does this topic fit into the greater picture of evolution?
- Founders effect: This example ties into the bigger picture of evolution because the increased frequency of this condition in the Amish population is all due to a reduced genetic variation. A small population broke off from a larger population to colonize America. If some of the colonizers are carriers for the disease or homozygous recessive, the prevalence of the recessive allele will be quite dramatic.
- Bottleneck effect: As shown by the graph by reasearchgate.net, the seal population has luckily rebounded, but the bottleneck effect significantly reduced their genetic variation. The scientific american blog provides a good explanation on this. They state that the few individuals that survived interbred and passed on their genes to their offspring. In the long run, inbreeding and lack of genetic diversity will often result in higher incidence of harmful mutations due to a disproportionate distribution of alleles.
- Overall, both of these effects explain how genetic drift causes big losses of genetic variation for small populations, leading to evolution.
Thank you for listening to this episode of My AP Biology Thoughts. For more student-ran podcasts, make sure that you visit www.hvspn.com. Thanks for listening!
Music Credits:
- “Ice Flow” Kevin MacLeod (incompetech.com)
- Licensed under Creative Commons: By Attribution 4.0 License
- http://creativecommons.org/licenses/by/4.0/
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