Presentation on theme: "Natural selection Essential Question: What mechanisms have allowed for diversity in organisms?"— Presentation transcript:
1Natural selectionEssential Question: What mechanisms have allowed for diversity in organisms?
2Breeding BunniesIn this investigation you will examine natural selection and genetic drift in a small population of wild rabbits.
3Breeding BunniesHypothesis: Record a hypothesis for how natural selection affects gene frequency in the population of wild rabbits over several generations.
4Breeding BunniesPredict: State what you would predict (if your hypothesis is supported) about the frequency of G alleles and g alleles in the population of rabbits after 10 generations, where gg bunnies are selected against (do not survive).
5Breeding Bunnies – Data Analysis How do you calculate the frequency of alleles?Frequency of G = G/total # of allelesFrequency of g = g/total # of allelesThe sum of the frequencies should = 1
6Breeding Bunnies – Data Analysis Frequency of Alleles in a Population of Wild Rabbits over 10 GenerationsFrequency of allele# of generations
7Breeding Bunnies – Analysis Was your original hypothesis supported by the data? Explain.How does the number and frequency of alleles for the dominant characteristic compare with the number of alleles for the recessive characteristic?The change in the frequency of alleles is called genetic drift. Why is genetic drift more likely to occur in smaller populations?Why does genetic drift occur in the first place?
8Breeding Bunnies – Analysis In a real rabbit habitat new animals often come into the habitat (immigrate), and others leave the area (emigrate). How might emigration and immigration affect the gene frequency of G and g in this population of rabbits?How could you simulate migration if you were to repeat this activity?How do your results compare with the class data? If different, why are they different?
9Breeding Bunnies – Analysis How are the results of this simulation an example of evolution?What are the key components of natural selection? What kinds of limited resources can create a struggle between individuals in a population? What kinds of variable traits (other than fur or lack of) within a population might natural selection act upon? How does natural selection affect the genetic variation within the next generation of the same population?
10What is Evolution?Change in Gene Frequencies over time due to random processes (Refined definiton)Mechanisms of EvolutionGenetic driftGene flowMutationNatural selection
11Mechanisms for Evolution – Genetic Drift Can be independent of natural selectionMay result in decrease in genetic diversityFounder effect – Blue Fugates of KentuckyBottleneck effect – FL PanthersFounder effect - French orphan Martin Fugate was born with Methemoglobinemia in which their bodies have a higher than normal form of hemoglobin called methemoglobin that a decreased ability to bind oxygen. He traveled to the United States in the early 1800s to obtain a land grant and improve his life. He didn’t want to stay in France since he felt like an outsider and was never adopted as a child. He later settled in Troublesome Creek with his red headed American bride, Elizabeth Smith. The two settled and had seven children, all of whom inherited Martin and Elizabeth’s rare recessive gene. Four of the children visibly showed this gene with their blue skin. Martin himself had dark blue skin.Bottleneck effect - The Florida panther once ranged throughout the southeastern United States but its numbers were drastically reduced from years of persecution and habitat destruction until the only remaining members that survived were in south Florida. In the early 1970’s the panther went through a genetic bottleneck, barely escaping extinction, and it’s hypothesized there may have been only 6 individuals in the population (Culver et al, 2008). This very lower number lead to severe inbreeding that caused several maladies.
12Mechanisms for Evolution – Gene Flow MigrationImmigration – moving into a populationEmigration – moving out of a populationIncrease in gene flow between 2 populations can lead to having more similarities between populaitons – less diversityDecrease in gene flow can lead to speciation
13Mechanisms for Evolution – mutations Changes in the structure of genes and chromosomesThe origin of all new allelesIncreases variationsMake extinction less likelyMostly random events
14Mechanisms for Evolution - Natural Selection Four requirements for natural selection to occurOrganisms produce more offspring than can surviveOrganisms have heritable traitsLimited resources leads to a struggle for existenceOrganisms having traits that are better suited for a particular environment are more likely to survive and reproduceAsk for a definition of the term heritable.
15Survival of the Fittest - What is Fitness? NO!Biggest?Fastest?Strongest?Prettiest?Furriest?Give students the opportunity to share with elbow partner their definition of the term “fitness.”Take a poll by show of handsBiggest?Fastest?Strongest?Prettiest?Furriest?
16?!Provide students with copies of cartoon. After providing them with an opportunity to read it, ask them if they’d like to revise their definition of “fitness.”Elicit response from volunteer and providing the correct response if you don’t get one – the ability to produce offspring.
17Survival of the Fittest – Quick Write Why is the phrase “survival of the fittest” a misrepresentation of Darwin’s concept of evolutionary fitness?