Biology Reference
In-Depth Information
degree of genetic differentiation among populations, and migration. Extensive
protein (allozyme) variation has been found in some natural insect populations.
Exceptions often include haplo-diploid Hymenoptera and clonal organisms such
as aphids (
Crozier 1977, Lester and Selander 1979, Murphy et al. 1990
). Even
for other insects, however, allozyme studies may underestimate the amount of
variation, detecting only
≈
30% of the actual genetic diversity as determined by
DNA-based methods.
Protein electrophoresis is a cost-effective technique and is relatively easy
to perform. For example, allozyme variability was used to identify Japan as
the likely origin of the mosquito
Aedes albopictus
that recently colonized the
United States and Brazil (
Kambhampati et al. 1991
). Allozymes were used to
demonstrate genetic differentiation between sympatrically occurring haw-
thorn and apple populations of
Rhagoletis pomonella
(
Feder et al. 1988
).
Unfortunately, protein electrophoresis may not detect sufficient variation to
answer some questions, and the number of analyses that can be performed with
very small insects may be limited because of inadequate amounts of proteins
(
Table 13.1
). Proteins are less stable than DNA and thus may be more sensitive to
handling and storage problems.
13.5.3 Amplified Fragment Length Polymorphisms (AFLP-PCR)
AFLP is a PCR-based method to develop large numbers of markers for popula-
tion analyses (
Mueller and Wolfenbarger 1999
, see Chapter 8). AFLP-PCR is a
relatively inexpensive and reliable method of identifying many genetic markers
without requiring DNA sequence information. As with RAPD-PCR and microsat-
ellite analyses, AFLP-PCR screens multiple different regions of the genome. AFLP
markers have been useful for assessing genetic differences among individuals,
populations, and species (
Mueller and Wolfenbarger 1999
). AFLP markers may
be more easily replicated than RAPD-PCR, although AFLP-PCR is more difficult to
use and develop (
Table 13.1
).
13.5.4 Double-Strand Conformation Polymorphism (DSCP)
DSCP is used to detect single-base changes in DNA. DSCP is detected by dif-
ferences in electrophoretic mobility in nondenaturing acrylamide gels of
double-stranded DNA (
Hagerman 1990, Saad et al. 1994, Atkinson and Adams
1997
). Single-base changes in the DNA may alter the curvature of the helical
axis of ds DNA, that could lead to changes in electrophoretic mobility. Not
all mutations affect DNA curving, so some are undetected by this approach
(
Table 13.1
).
