Measuring genetic diversity in natural populations

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Measuring genetic diversity in natural populations
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Protein electrophoresis, or allozyme
electrophoresis the earliest widely-used method
for screening population genetic diversity
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• Heterozygotes
• Heterozygosity (H) 8/20 0.40

• Allozyme Electrophoresis
• Each enzyme protein (this is phosphoglucomutase)
  is the product of a single genetic locus
• Different genetic forms of the enzyme at this
  locus appear as bands on the gel these are
  called allozymes
• Allozymes are inherited as Mendelian codominant
  alleles at each locus

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DNA fragments that are used to detect variation
are also separated and analyzed using gel
electrophoresis.
This gel shows the DNA fragments from an assay
for Restriction Fragment Length Polymorphism
(RFLP). RFLPs, like all DNA-based assays for
genetic variation, reveal much more diversity
than seen when screening allozymes.
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This gel shows three possible genotypes at the
CCR5 coreceptor locus DNA fragments from this
locus are produced by PCR amplification, followed
by restriction enzyme digestion
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Restriction enzyme digestion of the wild type
allele (no deletion) produces a 403 bp and a 332
bp fragment The ?32 allele contains a 32 bp
deletion, transforming the 403 to a 371 bp
fragment
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Calculating allele frequencies at the CCR5 locus
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(No Transcript)
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Patterns of genetic diversity

• clinal variation

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from Volpe and Rosenbaum (2000), p. 110
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Allozyme variation at the alcohol dehydrogenase
(Adh) locus in D. melanogaster Nearly all
populations are polymorphic for the slow AdhS and
fast AdhF alleles In Australia (and 2 other
continents) the locus shows a clineincrease in
frequency of AdhS towards the equator
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The mummichog Fundulus heteroclitus shows clinal
variation at lactate dehydrogenase-B Ldh-Bb
increases towards the north This allozyme has a
higher catalytic efficiency at lower temperatures
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Allozyme surveys show that variation is nearly
universal in humans and natural populations of
animals and plants The average individual is
heterozygous at 4-15 of its allozyme loci
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DNA sequence surveys reveal even more genetic
variation
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In 15,000 cystic fibrosis patients (homozygous at
CFTR) 30,000 different chromosomes 500
loss-of-function alleles