14. Role of Genetics in Conservation Biology
233
determination, and intraspecific genetic isolation among populations. Genetic
markers with moderate evolutionary rates (e.g., allozymes, mtDNA control region) are used to resolve genetic distances at intermediate taxonomic levels.
Resolution of deep branching patterns or divergence among distantly related taxa
requires highly conserved regions (e.g., ribosomal RNA genes) within which
evolutionary changes accumulate slowly (for reviews, see Moritz et al. 1987;
Avise 1994; Simon et al. 1994; Avise et al. 1995). Following is a brief introduction
to commonly used genetic tools and some examples of application in conservation
biology (see Avise and Hamrick [1996] for an excellent recent collection of case
studies in conservation genetics).
Protein Electrophoresis (Lewontin and Hubby 1966)
Electrochemical differences among proteins allow separation in either starch or
acrylamide gels. The net charge, size, and shape of the protein determine the speed
and direction of movement through a gel matrix in an electric field, and the
position of each protein is visualized with specific histochemical stains. Homozygous and heterozygous genotypes are detected as single and double bands for
monomeric proteins; polymeric proteins show more than two bands for heterozygotes. The quick and inexpensive resolution of genetic variation associated with
unlinked loci and the Mendelian inheritance of allozyme polymorphisms made
protein electrophoresis a good tool to assay heterozygosity within and between
populations and estimate gene flow (Koehn and Eanes 1978; Selander and Whittam 1983; Philipp and Gross 1994).
Among vertebrates, however, the level of protein polymorphism is frequently
too low to resolve specific genetic issues such as parentage. Molecular analysis of
nuclear or mtDNA markers replaces protein electrophoresis in such cases (Gilbert
et al. 1991; Packer et al. 1991; Sherwin et al. 1991; Martin et al. 1992a, b). There
are numerous applications of this technique in conservation biology, including the
identification of gene pools to guide conservation priorities, establishment of
restocking programs, and evaluation of causes of decline in endangered species
(e.g., Vrijenhoek et al. 1985; Quattro and Vrijenhoek 1989; Wayne et al. 1991;
Petit et al. 1998).
DNA-DNA Hybridization
The complementary strands of the DNA duplex are connected by hydrogen bonds
that are unstable at high temperatures and become single stranded when boiled.
With cooling temperature, the complementary nucleotide sequences reanneal (i.e.,
become double stranded). In general, the greater the similarity or homology
between DNA sequences, the more hydrogen bonds exist between matched nucleotides and the greater the thermal stability of the DNA duplex. To determine
the homology of DNA sequences, single-stranded DNA of two individuals is
allowed to anneal. DNA-DNA hybridization simultaneously samples genetic
differences across most of the genome and hence provides valuable genetic
233
determination, and intraspecific genetic isolation among populations. Genetic
markers with moderate evolutionary rates (e.g., allozymes, mtDNA control region) are used to resolve genetic distances at intermediate taxonomic levels.
Resolution of deep branching patterns or divergence among distantly related taxa
requires highly conserved regions (e.g., ribosomal RNA genes) within which
evolutionary changes accumulate slowly (for reviews, see Moritz et al. 1987;
Avise 1994; Simon et al. 1994; Avise et al. 1995). Following is a brief introduction
to commonly used genetic tools and some examples of application in conservation
biology (see Avise and Hamrick [1996] for an excellent recent collection of case
studies in conservation genetics).
Protein Electrophoresis (Lewontin and Hubby 1966)
Electrochemical differences among proteins allow separation in either starch or
acrylamide gels. The net charge, size, and shape of the protein determine the speed
and direction of movement through a gel matrix in an electric field, and the
position of each protein is visualized with specific histochemical stains. Homozygous and heterozygous genotypes are detected as single and double bands for
monomeric proteins; polymeric proteins show more than two bands for heterozygotes. The quick and inexpensive resolution of genetic variation associated with
unlinked loci and the Mendelian inheritance of allozyme polymorphisms made
protein electrophoresis a good tool to assay heterozygosity within and between
populations and estimate gene flow (Koehn and Eanes 1978; Selander and Whittam 1983; Philipp and Gross 1994).
Among vertebrates, however, the level of protein polymorphism is frequently
too low to resolve specific genetic issues such as parentage. Molecular analysis of
nuclear or mtDNA markers replaces protein electrophoresis in such cases (Gilbert
et al. 1991; Packer et al. 1991; Sherwin et al. 1991; Martin et al. 1992a, b). There
are numerous applications of this technique in conservation biology, including the
identification of gene pools to guide conservation priorities, establishment of
restocking programs, and evaluation of causes of decline in endangered species
(e.g., Vrijenhoek et al. 1985; Quattro and Vrijenhoek 1989; Wayne et al. 1991;
Petit et al. 1998).
DNA-DNA Hybridization
The complementary strands of the DNA duplex are connected by hydrogen bonds
that are unstable at high temperatures and become single stranded when boiled.
With cooling temperature, the complementary nucleotide sequences reanneal (i.e.,
become double stranded). In general, the greater the similarity or homology
between DNA sequences, the more hydrogen bonds exist between matched nucleotides and the greater the thermal stability of the DNA duplex. To determine
the homology of DNA sequences, single-stranded DNA of two individuals is
allowed to anneal. DNA-DNA hybridization simultaneously samples genetic
differences across most of the genome and hence provides valuable genetic