Biology Reference
In-Depth Information
analysis, mitochondrial DNA (mtDNA) analysis, chloroplast DNA
(cpDNA) analysis, and sequencing of DNA and RNA genes or sectors.
DNA analysis, in particular, is an active and rapidly developing field.
Allozyme Analysis
The oldest and least expensive form of genetic analysis is enzyme elec-
trophoresis, a technique for detecting variation in the genes coding par-
ticular enzymes. Allozymes are different forms of an enzyme coded by
different alleles at a single genetic locus. From 20 to 40%, or sometimes
more, of the loci coding enzymes show variability in different groups of
organisms (Parker et al. 1998). Allozyme analysis can detect patterns of
heterozygosity as well as allele frequencies.
For an allozyme analysis, enzymes are first extracted from macerated
tissue. The extract is then placed in a starch gel, cellulose acetate gel, or
other gel medium and subjected to electrophoresis. An electrophoretic
gradient is created by placing the gel in contact with two trays contain-
ing a buffer solution and connected to a power source. Several buffer
solutions may be used, depending on the enzymes chosen for analysis. In
the electrophoretic gradient, different molecular forms of enzymes
migrate through the gel at different rates. After migration has occurred,
an enzyme-specific stain is applied to the gel to define bands correspond-
ing to the points to which different enzyme forms have migrated.
Allozyme analyses are usually carried out on many enzymes.The number
of different forms present in individuals or populations can thus be deter-
mined for each enzyme, and variability within and among populations
can be evaluated from results for all enzyme analyses.
DNA Fragment Length Polymorphism Analyses
DNA fragment length polymorphism analyses are based on the action of
restriction enzymes, which cut double-stranded DNA at points where a
specific sequence of four to eight nucleotides occurs (Parker et al. 1998).
DNA is first extracted from the plant or animal material. One or several
restriction enzymes are then used to cut the DNA into fragments. Differ-
ences due to nucleotide substitutions, additions, subtractions, or
rearrangements may exist within these fragments. Depending on the
objective of the analysis and knowledge of specific gene structure, various
approaches may be followed to detect these differences.
