Biology Reference
In-Depth Information
1994, Toth et al. 2000
). Microsatellites mutate at a high rate and are thought to
play a significant role in genome evolution by creating and maintaining quan-
titative genetic variation (
Kashi et al. 1997
). For example, when microsatellites
are found in promoter regions, they may influence transcriptional activity. The
length of microsatellites could also affect protein-protein interactions during
transcription.
Two models were proposed to account for the high mutation rate in micro-
satellites. The first model, DNA polymerase slippage, assumes that replicating
DNA strands transiently disassociate and then reassociate in a misaligned form,
which will result in length and sequence variations. The second model involves
unequal recombination to produce mutations in microsatellites. Understanding
the evolution of microsatellites is considered important in using them for eco-
logical analyses.
Microsatellite analysis results in a pattern of DNA bands on gels that resem-
ble “bar codes” used to identify items in stores. DNA fingerprinting can be used
to evaluate DNA variability at the individual and population level and was first
conducted on humans and other vertebrates (
Jeffreys 1987
). The banding pat-
terns produced often are specific to a particular individual (except for mono-
zygotic twins), are inherited in a Mendelian manner, and are generally stable
within an individual's germ-line and somatic tissues. Polymorphisms are visual-
ized by hybridizing a labeled probe to genomic DNA that has been cut with a
restriction enzyme and separated into bands on a gel by electrophoresis.
Microsatellite markers can identify individual insects, or their progeny, evalu-
ate kinship, resolve whether a mating has been successful, and reveal differen-
tiation among closely related populations in the field (
Burke 1989, Wang et al.
1999
). Microsatellites could be useful in monitoring establishment and disper-
sal of specific biotypes, including those with low levels of protein variation such
as parthenogenetic aphids or hymenopteran parasitoids (
Table 13.1
). Analysis
of microsatellites has become a popular method for identifying high levels of
genetic variability.
Unfortunately, microsatellite sequences usually differ in different species,
even closely related species. This means that microsatellite sequence data usually
must be obtained for each species under study, making microsatellites relatively
time consuming and expensive to develop. Furthermore, different taxonomic
groups may exhibit differences in the ease with which microsatellites can be
isolated (
Neve and Meglecz 2000
). For example there were only five microsatel-
lite studies published on Lepidoptera between 1997 and 1999, but 47 were pub-
lished on Hymenoptera (
Neve and Meglecz 2000
); it is not clear whether equal
