Biology Reference
In-Depth Information
Chloroplast DNA Analysis
Chloroplast DNA is a maternally inherited genome in most higher plants
and, like mtDNA, does not undergo recombination during plant repro-
duction. Chloroplast DNA is larger than mtDNA; it is estimated at
120,000-150,000 base pairs in many plants. Chloroplast DNA accumu-
lates mutations more slowly than does nuclear DNA, however. Analysis is
carried out by sequencing or use of the RFLP or RAPD techniques.
DNA and RNA Sequencing
Genes or segments of DNA or RNA can be captured by primers and
amplified as in AFLP analyses.The specific nucleotide sequences of these
units can then be determined by standard sequencing procedures (Kraw-
czak and Schmidke 1998).
Founder Effects and Genetic Bottlenecking
Genetic variability among alien species varies greatly.When introductions
involve only a few founder individuals from a limited part of their native
range, only a fraction of the genetic variability of the source population
is introduced.This “founder effect” may be compounded by genetic drift
that leads to the loss of alleles from small founder populations. When a
founder population remains small over several to many generations, the
loss of genetic variability by genetic drift, termed genetic bottlenecking,
may lead to loss of almost all variation in the population (Allendorf 1986).
Thus, the size of the founding population and how quickly this popula-
tion increases are important determinants of the genetic variability of
alien populations.
The European starling (
Sturnus vulgaris
) in North America provides a
good example of genetic bottlenecking and at the same time shows that
low genetic variability does not always limit the success of an alien
species. The North American population, now continent-wide in distri-
bution and enormously abundant, is derived from about 100 individuals
released in New York City in 1890 and 1891 (Cabe 1998). Allozyme
analysis showed that the North American population lacks about 42% of
the alleles that occur at loci showing variability in Europe. Furthermore,
starlings from different parts of North America show no significant vari-
ation in genetic makeup. Even without a high degree of genetic variabil-
