Transcript Mechanisms for Evolution - Ms. McGurr's Science Page

NATURAL SELECTION
Essential Question: What mechanisms have allowed
for diversity in organisms?
BREEDING BUNNIES
• In this investigation you will examine
natural selection and genetic drift in a small
population of wild rabbits.
BREEDING BUNNIES
• Hypothesis: Record a
hypothesis for how natural
selection affects gene
frequency in the population of
wild rabbits over several
generations.
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).
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
BREEDING BUNNIES – DATA ANALYSIS
Frequency of Alleles in a Population of Wild Rabbits over 10 Generations
1.0
0.9
Frequency of allele
0.8
0.7
0.6
0.5
Fur
0.4
No Fur
0.3
0.2
Generations
0.1
0.0
1
2
3
4
5
6
7
# of generations
8
9
10
BREEDING BUNNIES – ANALYSIS
1. Was your original hypothesis supported by the data?
Explain.
2. How does the number and frequency of alleles for the
dominant characteristic compare with the number of
alleles for the recessive characteristic?
3. The change in the frequency of alleles is called genetic
drift. Why is genetic drift more likely to occur in smaller
populations?
4. Why does genetic drift occur in the first place?
BREEDING BUNNIES – ANALYSIS
5. 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?
6. How could you simulate migration if you were to
repeat this activity?
7. How do your results compare with the class data? If
different, why are they different?
BREEDING BUNNIES – ANALYSIS
8. How are the results of this simulation an example of
evolution?
9. What are the key components of natural selection?
10. What kinds of limited resources can create a struggle
between individuals in a population?
11. What kinds of variable traits (other than fur or lack of)
within a population might natural selection act upon?
12. How does natural selection affect the genetic
variation within the next generation of the same
population?
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
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
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
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
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
SURVIVAL OF THE FITTEST - WHAT IS FITNESS?
• Biggest?
• Fastest?
• Strongest?
• Prettiest?
• Furriest?
NO!
?!
SURVIVAL OF THE FITTEST – QUICK WRITE
• Why is the phrase “survival of the fittest” a
misrepresentation of Darwin’s concept of
evolutionary fitness?