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Natural selection Essential Question: What mechanisms have allowed for diversity in organisms?

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Presentation on theme: "Natural selection Essential Question: What mechanisms have allowed for diversity in organisms?"— Presentation transcript:

1 Natural selection Essential Question: What mechanisms have allowed for diversity in organisms?

2 Breeding Bunnies In this investigation you will examine natural selection and genetic drift in a small population of wild rabbits.

3 Breeding Bunnies Hypothesis: Record a hypothesis for how natural selection affects gene frequency in the population of wild rabbits over several generations.

4 Breeding Bunnies Predict: 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).

5 Breeding Bunnies – Data Analysis
How do you calculate the frequency of alleles? Frequency of G = G/total # of alleles Frequency of g = g/total # of alleles The sum of the frequencies should = 1

6 Breeding Bunnies – Data Analysis
Frequency of Alleles in a Population of Wild Rabbits over 10 Generations Frequency of allele # of generations

7 Breeding 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?

8 Breeding 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?

9 Breeding 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?

10 What is Evolution? Change in Gene Frequencies over time due to random processes (Refined definiton) Mechanisms of Evolution Genetic drift Gene flow Mutation Natural selection

11 Mechanisms for Evolution – Genetic Drift
Can be independent of natural selection May result in decrease in genetic diversity Founder effect – Blue Fugates of Kentucky Bottleneck effect – FL Panthers Founder 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.

12 Mechanisms for Evolution – Gene Flow
Migration Immigration – moving into a population Emigration – moving out of a population Increase in gene flow between 2 populations can lead to having more similarities between populaitons – less diversity Decrease in gene flow can lead to speciation

13 Mechanisms for Evolution – mutations
Changes in the structure of genes and chromosomes The origin of all new alleles Increases variations Make extinction less likely Mostly random events

14 Mechanisms for Evolution - Natural Selection
Four requirements for natural selection to occur Organisms produce more offspring than can survive Organisms have heritable traits Limited resources leads to a struggle for existence Organisms having traits that are better suited for a particular environment are more likely to survive and reproduce Ask for a definition of the term heritable.

15 Survival 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 hands Biggest? 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.

17 Survival of the Fittest – Quick Write
Why is the phrase “survival of the fittest” a misrepresentation of Darwin’s concept of evolutionary fitness?

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