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Set up Cornell Notes on pg. 23 •Topic: Other Mechanisms of Evolution: Genetic Drift •Essential Question: 1. How does gene flow affect neighboring populations? 2. Would a population of 10 individuals or 100 individuals be more vulnerable to genetic drift. Why? 11.3 OtherIons, Mechanisms of Evolution: 2.1 Atoms, and Molecules Genetic Drift 1. How does gene flow affect neighboring populations? 2. Draw a “Picture Tree Map” on pg.22 describing the two processes through which genetic drift can occur 11.3 Other Mechanisms of Evolution Objectives 8 c: Students know the effects of genetic drift on the diversity of organisms in a population. 11.3 Other Mechanisms of Evolution KEY CONCEPT Natural selection is not the only mechanism through which populations evolve. 11.3 Other Mechanisms of Evolution Gene flow is the movement of alleles between populations. • Occurs when individuals join new populations and reproduce •Its alleles become part of that new population’s gene pool •The alleles are removed from its former population •Increases genetic variation in the receiving population! Population 1 in Florida Population 2 in Maine 11.3 Other Mechanisms of Evolution Leaving population #1 Joining population # 2 2 miles away 11.3 Other Mechanisms of Evolution • Gene flow keeps neighboring populations similar. • The less gene flow that occurs, the more genetically different the two populations will become • Low gene flow increases the chance that two populations will evolve into different species. 11.3 Other Mechanisms of Evolution • If I asked you to randomly pick 100 flowers from this field what percentage of each color would you expect to pick? • What if I asked you to choose 10? • Would it always be 50/50? • NO! You could pick 90 red and 10 pink. Unlikely, but it could happen. 1000 pink and 1000 red flowers in the population 11.3 Other Mechanisms of Evolution • Genetic drift is a change in allele frequencies due to CHANCE and causes a LOSS of genetic diversity *It is most common in small populations Generation #1 Generation #2 11.3 Other Mechanisms of Evolution Genetic Drift Activity: • You are working with a very small population of rabbits • 6 Rabbits in total- 3 white and 3 black • Over each generation, you should see the genetic diversity decrease over time due to random mating 11.3 Other Mechanisms of Evolution There are two types of Genetic Drift: 1. Bottleneck Effect 2. Founder Effect Effects of Genetic drift: • Populations lose genetic variation • With little variation, a population is less likely to have some individuals that will be able to adapt to a changing environment • Any lethal alleles may be carried in the population by heterozygous individuals, and become more common in the gene pool due to chance alone 11.3 Other Mechanisms of Evolution On pg. 22 create a Picture Tree map on the two types of Genetic Drift Genetic Drift Bottleneck Effect Founder Effect • . • . • . • . • . • . • Real Life Example • Real Life Example PICTURE PICTURE 11.3 Other Mechanisms of Evolution • A population bottleneck event can lead to genetic drift. – It occurs when an event drastically reduces population size. Original population –The bottleneck effect is genetic drift that occurs after a bottleneck event. Leaves very little genetic variation 11.3 Other Mechanisms of Evolution Genetic Drift: Bottleneck Effect: Northern Elephant Seals –During the 1800s the over hunting of Northern Elephant seals reduced the population to about 20 individuals –The 20 seals did not represent the genetic diversity of the original population –Since hunting stopped, the population has grown to over 100,000 –However the population has little genetic diversity 11.3 Other Mechanisms of Evolution The founder effect is genetic drift that occurs after the start of new population. – It occurs when a few individuals start a new population 11.3 Other Mechanisms of Evolution Genetic Drift: Founder Effect: The Amish of Lancaster PA • Amish communities founded in N. America by small #s of migrants from Europe • Amish in PA have a high rate of Ellis-van Creveld Syndrome • This dwarfism is rare in other human populations, but more common in Amish populations • Can trace it back to one of the community’s founding couples Set up Cornell Notes on pg. 25 •Topic: 11.3 Other Mechanisms of Evolution: Sexual Selection •Essential Question: 1. How can mating have an important effect of the evolution of populations? 2. Traits that increase mating success are not always adaptive for the survival of the individual (Red or blue feathers). How can these traits evolve if it makes them easily spotted by predators? 11.3 OtherIons, Mechanisms of Evolution: 2.1 Atoms, Sexual Selection and Molecules 1. How can mating have an important effect of the evolution of populations? 2. Traits that increase mating success are not always adaptive for the survival of the individual (Red or blue feathers). How can these traits evolve if it makes them easily spotted by predators? 11.3 Other Mechanisms of Evolution Mating can have an important effect on the evolution of populations • Both sexes benefit from having offspring that survive 11.3 Other Mechanisms of Evolution Sexual selection occurs when certain traits increase mating success. • Sexual selection occurs due to higher cost of reproduction for females. – males produce many sperm continuously – females are more limited in potential offspring each cycle * This makes females choosy about mates! 11.3 Other Mechanisms of Evolution • There are two types of sexual selection. – intrasexual selection: competition among males Ex: head butting of Bighorn sheep –intersexual selection: males display certain traits to females Ex: Male peacocks fanning out their tails Sexual Selection Video Notes: • Which trait increases mating success? • It is intrasexual or intersexual selection? • Vogelkop Bowerbird: • Hummingbird: • Red deer: • Capercaillie: • Ibex: • Mudskipper: Sexual Selection of Guppies In books on page 339 • Read the example • Complete the 3 questions about the guppy tail size experiment on pg. 24 in your I.N.B.