Download Genetic variation - People Server at UNCW

Measuring genetic diversity in
natural populations
Protein electrophoresis,
or allozyme
electrophoresis: the
earliest widely-used
method for screening
population genetic
diversity
*
* *
* **
*
• 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
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.
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
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
Calculating allele frequencies
at the CCR5 locus
European Number of +/+ +/32 32/32
population people tested
Ashkenazi
43
26
16
1
Iceland
102
75
24
3
Britain
283
223
57
3
Patterns of genetic diversity
clinal variation
from Volpe and Rosenbaum
(2000), p. 110
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 cline—increase
in frequency of AdhS
towards the equator
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
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
DNA sequence surveys reveal even more
genetic variation
In 15,000 cystic fibrosis patients (homozygous at CFTR):
30,000 different chromosomes
500 loss-of-function alleles