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Population
Group of individuals of the same species that live in the same area, interbreed to produce fertile offspring
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Evolution
A change in allele frequencies in a population from generation to generation
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Hardy-Weinberg Equilibrium
- When allele frequencies are stable
- Use allele/genotype frequencies within a generation and probability to determine if population is likely evolving
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For allele frequencies of a population to remain the same, what conditions would have to be present?
- No mutations
- No natural selection (no phenotypes outperform others in the population's environmental conditions?
- Extremely large population size (no genetic drift)
- No gene flow
- Random mating (all individuals have an equal chance of passing on their alleles, no individual more likely to mate based on their alleles/phenotype)
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What is happening when you observe changes in allele frequency from generation to generation?
You know that at least 1 of these mechanisms of evolution is occurring
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Gene Pool
All copies of every (or a specific) gene in a population-- alleles for a specific gene
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Allele Frequency
- Percentage of a given allele in a population
- Always add up to 1 (all of the alleles=100% of the alleles in a population)
- p: frequency of dominant allele
- q: frequency of recessive allele
- p+q=1
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Focus on 1 gene: CR=red, CW=white, incomplete dominance
Frequency of CR=0.8= p
Frequency of CW=0.2= q
What does this mean with random mating?
- 80% chance each egg and sperm will have CR
- 20% chance each egg and sperm will have CW
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Hardy-Weinberg equation
- All genotype frequencies also have to add up to 1
- Gives genotype frequencies of a population if evolution is NOT occurring
- 1= p2 + 2pq + q2
- p2= f(CRCR)
- 2pq= f(CRCW)
- q2= f(CWCW)
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Population Level Punnett Square
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In a population of 100, how many CRCR, CRCW, and CWW individuals would you observe if the population is not evolving?
A) 64 C RC R, 16 C RC W, 4 C WC W
B) 64 C RC R, 32 C RC W, 4 C WC W
C) 64 C RC R, 32 C RC W, 40 C WC W
D) 32 C RC R, 64 C RC W, 4 C WC W
What would happen if the ratio was 70 C RC R, 20 C RC W, 10 C WC W
B) 64 CRCR, 32 CRCW, 4 CWCW
The population would most likely be evolving since there is a change
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Hardy-Weinberg Steps:
- Calculate p and q (observed allele frequencies) from observed genotype frequencies
- Use observed p and q values to calculate expected genotype frequencies
- Use observed genotype to calculate observed genotype frequencies
- Compare observed and expected genotype frequencies
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What does it mean when the observed genotype frequencies and expected genotype frequencies match?
This indicates that the population isn't evolving
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