Population%20Genetics

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Population Genetics
Population Genetics
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Populations

• A group of the same species living in an area
• No two individuals are exactly alike (variations)
• More Fit individuals survive pass on their
  traits

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Modern Synthesis Theory

• Combines Darwinian selection and Mendelian
  inheritance
• Population genetics - study of genetic variation
  within a population
• Emphasis on quantitative characters

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Modern Synthesis Theory

• Todays theory on evolution
• Recognizes that GENES are responsible for the
  inheritance of characteristics
• Recognizes that POPULATIONS, not individuals,
  evolve due to natural selection genetic drift
• Recognizes that SPECIATION usually is due to the
  gradual accumulation of small genetic changes

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Microevolution

• Changes occur in gene pools due to mutation,
  natural selection, genetic drift, etc.
• Gene pool changes cause more VARIATION in
  individuals in the population
• This process is called MICROEVOLUTION
• Example Bacteria becoming unaffected by
  antibiotics (resistant)

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The Gene Pool

• Members of a species can interbreed produce
  fertile offspring
• Species have a shared gene pool
• Gene pool all of the alleles of all individuals
  in a population

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Allele Frequencies Define Gene Pools
500 flowering plants
480 red flowers
20 white flowers
320 RR
160 Rr
20 rr
As there are 1000 copies of the genes for color,
the allele frequencies are (in both males and
females) 320 x 2 (RR) 160 x 1 (Rr) 800 R
800/1000 0.8 (80) R 160 x 1 (Rr) 20 x 2 (rr)
200 r 200/1000 0.2 (20) r
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Gene Pools

• A populations gene pool is the total of all
  genes in the population at any one time. 
• Each allele occurs with a certain frequency (.01
  1).

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The Hardy-Weinberg Theorem

• Used to describe a non-evolving population.
• Shuffling of alleles by meiosis and random
  fertilization have no effect on the overall gene
  pool. 
•  Natural populations are NOT expected to actually
  be in Hardy-Weinberg equilibrium.

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The Hardy-Weinberg Theorem

• Deviation from Hardy-Weinberg equilibrium usually
  results in evolution
• Understanding a non-evolving population, helps us
  to understand how evolution occurs

•                        
• .

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Sources of genetic variation(Disruption of H-W
law)

• Mutations- if alleles change from one to
  another, this will change the frequency of those
  alleles
• 2. Genetic recombination - crossing over
  independent assortment
• 3. Migration - immigrants can change the
  frequency of an allele by bringing in new alleles
  to a population.
• - emigrants can change allele frequencies by
  taking alleles out of the population

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Sources of genetic variation(Disruption of H-W
law)

• 4. Genetic Drift- small populations can have
  chance fluctuations in allele frequencies (e.g.,
  fire, storm).
• - bottleneck founder effect
• 5. Natural selection- if some individuals
  survive and reproduce at a higher rate than
  others, then their offspring will carry those
  genes and the frequency will change for the next
  generation.

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Hardy-Weinberg Equilibrium                        
             The gene pool of a non-evolving
population remains constant over multiple
generations i.e., the allele frequency does not
change over generations of time.   The
Hardy-Weinberg Equation                          
             1.0 p2 2pq q2                  
                               where p2
frequency of AA genotype 2pq frequency of Aa
plus aA genotype q2 frequency of aa genotype
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