13.6 to 13.8. PopulationSpecies A group of interacting individuals belonging to one species and...
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Transcript of 13.6 to 13.8. PopulationSpecies A group of interacting individuals belonging to one species and...
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LEQ: How has knowledge of genetics influenced modern
ideas about evolution?13.6 to 13.8
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Populations are units of evolution
Population Species
A group of interacting individuals belonging to one species and living in the same geographic area
A group whose members possess similar anatomical characteristics and have the ability to interbreed
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Populations are units of evolution
Population Genetics Modern Synthesis
The study of genetic changes in populations; the science of microevolutionary changes in a population
A comprehensive theory of evolution that incorporates genetics and includes most of Darwin’s original ideas, focusing on populations as the fundamental units of evolution (individuals don’t evolve – populations do)
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Populations are the units of evolution
Gene Pool Example
All of the alleles for all of the loci in all individuals in a population
Each allele has a frequency in the population
Example: you have a wild boar population in which 50 percent of the alleles for a particular gene are dominant (B) and 50 percent of the alleles for the gene are recessive (b).
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Populations are units of evolution
Microevolution example
A change in a populations gene pool over a succession of generations; evolutionary changes in species over relatively brief periods of geologic time
Change in the allele frequency over time
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The gene pool of nonevolving populations remains constant…
Hardy Weinberg Equilibrium
5 Conditions of Hardy Weinberg
Named for 2 men who figured out that the shuffling of genes that occurs during sexual reproduction, by itself, cannot change the overall genetic make-up of a population
p + q = 1 (p = dominant allele frequency / q = recessive allele frequency)
p2 + 2pq + q2 = 1 ( p2 = homo dominant; 2pq = hetero; q2 = homo recessive)
1. Large population2. No migration in or out3. Mutations do not alter
gene pool4. Random mating5. Natural selections
does not occur (all have equal chance to survive)
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Hardy Weinberg equation is useful in public health science
PKU – autosomal recessive trait
About 1 in 10,000 babies born in the US have PKU
How many people are carriers?
First step: calculate q2 (individuals with PKU / homo recessive)◦ q2 = 1/10,000 = 0.0001
Solve for q (the frequency of the recessive allele in the population)◦ q = q2 = 0.01
Use the equation “p + q = 1” to solve for p.◦ p = 0.99
Use the equation “p2 + 2pq + q2 = 1” and solve for carrier genotype.◦ 2pq = 2(.99)(.01)
= .0198◦ ~2% of the population
are carriers
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Example #2
Try it yourself Answer
You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following:◦ The frequency of the "aa"
genotype.◦ The frequency of the "a" allele.◦ The frequency of the "A" allele.◦ The frequencies of the
genotypes "AA" and "Aa."◦ The frequencies of the two
possible phenotypes if "A" is completely dominant over "a."
q2 = .36 q = .6; frequency of “a”
allele is 60% p = .4; frequency of “A”
allele is 40% p2= .16; frequency of AA
is 16% 2pq = .48; frequency of
Aa is 48% Frequency of A
phenotype is 64% Frequency of a
phenotype is 36%