Evolution Part 1
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Transcript of Evolution Part 1
Evolution Part 1
BIOL 1407
Evolution
• Heritable genetic change in populations or groups of populations over time
• Changes in gene pool
Evolution
• Also includes populations diverging from one another over time
may lead to new species
Mechanisms of Evolution
• Genetic Drift– Population Bottlenecks– Founder Effect
• Gene Flow– Immigration– Emigration
• Mutations• Natural Selection
Genetic Drift
• Changes in gene pool of populations due to random chance
Genetic Drift
Genetic Drift Image Credit: UC Museum of Paleontology's Understanding Evolution www.evolution.berkeley.edu
Genetic Drift
• Genetic drift has a bigger effect on small populations.
Bottleneck Effect
• Changes in gene pool of populations due to some event
drastically reduces population
Bottleneck Effect
• Survival is random
• Whether an organism survives does not depend on any characteristic (allele)
Example of Bottleneck Effect
• Population of plants on a mountain side
• An avalanche wipes out all but a patch of plants behind the shelter of a large outcrop.
Example of Bottleneck Effect
• Plants behind the outcrop survived only because they were out of the path of the avalanche.
• There was nothing about the plants’ genes that influenced survival.
Example of Bottleneck Effect
• Surviving population has an allele frequency different from the original population.
Bottleneck Effect
Bottleneck Effect: Cheetahs
• 10,000 years ago, cheetah populations worldwide crashed
• Due to climate change
• Photo Credit: Courtesy of Smithsonian National Zoo @ nationalzoo.si.edu
Cheetahs
• Only cheetahs in Africa & Eurasia survived
• Location, not genes Survival
• Photo Credit: Kevin Walsh, 2006, Wikimedia Commons
Cheetahs
• Cheetahs today: Genetically identical • Photo Credit: Lukas Kaffer, 2007, courtesy of Wikimedia Commons
Bottleneck Effect:Northern Elephant Seals
• Once numerous in the northern Pacific.
• 1800s: Hunted extensively for blubber
• Photo Credit: Michael Baird of bairdphotos.com, courtesy of Wikimedia Commons
Northern Elephant Seals
• Only 100-1000 animals in a Mexican colony survived
• Photo Credit: Michael Baird of bairdphotos.com, courtesy of Wikimedia Commons
Northern Elephant Seals
• Today: >100,000 individuals
• Very little genetic diversity
• Photo Credit: Mila Zinkova, 2008, courtesy of Wikimedia Commons
Founder Effect
• New population established by very small number of individuals (“founders”)
• By chance, founder group has a different allele mix than original population
Example of Founder Effect
• 200 German immigrants founded the Old Order Amish of Pennsylvania
• Photo credit: : Matthew Trump, 2004, Wikimedia Commons
Old Order Amish
• One couple brought allele polydactyly Six fingers and toes
• Photo credit: G. Baujat and M LeMerrer, 2007, Wikimedia Commons
Old Order Amish
• Inbreeding has frequency of polydactyly
• Click on this link:
http://www.pbs.org/wgbh/evolution/library/06/3/l_063_03.html
• Photo credit: gadjoboy, 2006, Wikimedia Commons
Gene Flow
• Movement of alleles between populations• Immigration: movement of alleles into a
population• Emigration: movement of alleles out of
population
Example of Gene Flow
• Transfer of pollen from one population of sunflowers into another population of sunflowers
• Photo Credit: Sunflower Pollen, Courtesy of Wikimedia Commons
Example of Gene Flow
• Male juvenile Belding’s ground squirrels emigrate from their birthing population to new populations.
• 40-70% emigrate as juveniles. Remaining males leave by the end of their first year.
• Photo Credit: Courtesy of Yathin at FlickR, http://www.flickr.com/photos/yathin/807378578/in/set-72157600812861150/
Mutations
• Mutations can add new alleles to a population
• Review this BIOL 1406 concept
• Photo Credit for black Eastern Fox Squirrel: Jeffrey Pippen, Duke University
• Photo Credit for wild-type Eastern Fox Squirrel: Calibas, 2007, Wikimedia Commons
Asexual Populations
• Mutations are primary source of genetic variation in asexual populations
• Photo Credit for E. coli 0157 colonies: Centers for Disease Control, 2005, Wikimedia Commons
Natural Selection
• Environment determines which genes are passed onto the next generation
• Based on which individuals successfully survive and reproduce
Natural Selection
• Requires: – Genetic Variation– Overproduction of Offspring– Struggle for Existence– Differential Survival and Reproduction
View video at: http://www.pbs.org/wgbh/evolution/library/11/2/e_s_4.html
Photo credit: Dean E. Briggins, U.S. Fish and Wildlife Service, http://www.nsf.gov/news/news_images.jsp?cntn_id=104263&org=LPA
Genetic Variation
• Organisms in the population vary in their characteristics
• Variations are heritable Passed from parents to offspring
Variation in Snail Shells
Flower Variations
Natural Selection
Flow Chart
How Natural
Selection Works
View “Pocket Mouse and Predation” at http://www.hhmi.org/biointeractive/evolution/animations.html
Photo Credit: Cheryl S. Brehme, USGS at http://soundwaves.usgs.gov/2006/02/pubs.html
View “Pocket Mouse Evolution” at http://www.hhmi.org/biointeractive/evolution/animations.html
Photo Credit: J. Harris, American Society of Mammalogy, at: http://www.mammalogy.org/mil_images/images/mid/752.jpgl
Artificial Selection
• Humans select which genes are passed onto the next generation
• Based on characteristics that humans find valuable or desirable
View “Dog Breeding” at http://www.hhmi.org/biointeractive/evolution/video.html
Photo credit: papillon.cz, courtesy of Wikimedia Commons (http://commons.wikimedia.org/wiki/Image:%21flowers.jpg)
View “Breeding Teosinte” at http://www.hhmi.org/biointeractive/evolution/video.html
Photo credit: USDA, 2005, courtesy of Wikimedia Commons
Another Example of Artificial Selection
Sexual Selection
• Some characteristics influence individual’s chance of mating
• Photo Credit: Ian Sewell, 2006, Wikimedia Commons
Sexual Selection
• Individual may have shorter life but will have better chances of mating and producing offspring
• Photo Credit: David Dennis, 2007, Wikimedia Commons
Types of Sexual Selection
• Mate Competition– One sex competes for access to the other
sex– Other sex always “chooses” winner
• Mate Choice– One sex chooses mate based on
characteristics of other sex
Example of Mate Competition
• Male bighorn sheep fight for mates
• Male with largest horns usually wins
• Photo Credit: Alan D. Wilson, naturespicsonline.com, courtesy of Wikimedia Commons
Video of Bighorn Sheep Fighting:http://www.youtube.com/watch?v=WKmGiSm3-2U
Photo Credit: Jon Sullivan, Wikimedia Commons
Example of Mate Choice
• Peacocks display their tails
• Females choose male with showiest tail
• Photo credit: Aaron Logan, www.lightmatter.net, courtesy of Wikimedia Commons
Example of Mate Choice
• Large tails decrease survival of peacocks
• Natural selection favors small tails
• Photo credit: Jörg Hempel, courtesy of Wikimedia Commons
Example of Mate Choice
• Peacocks with small tails do not mate
• Mate choice favors large tails
• Photo credit: Jyshah, 2007, courtesy of Wikimedia Commons
View the video at: http://www.pbs.org/wgbh/evolution/library/01/6/l_016_09.html
Photo credit: Myukii, courtesy of Wikimedia Commons
The End
Unless otherwise specified, all images in this presentation came from:
Campbell, et al. 2008. Biology, 8th ed. Pearson Benjamin Cummings.