Biology Reference
In-Depth Information
species can be distinguished but members of the same species have the same (or
nearly the same) DNA sequence.
The process of species identification is relatively straightforward [3]. DNA is
isolated from the unknown material and amplification primers are used to produce
a PCR product of around 400 bp in length [4, 5]. This product is sequenced and the
DNA sequence is compared with those on the DNA database. If there is a 100%
match to a DNA sequence from a registered species, and the next closest species has
a homology of 95%, then there is every reason to believe that the unknown material
is from the species to which it matched.
Another mitochondrial locus used in species testing in the cytochrome oxidase 1
gene. This locus is promoted by the Barcode for Life consortium [6] and is used
in exactly the same way as cytochrome b , only a section of 648 bp is used for the
comparison. Both the cytochrome b gene and the cytochrome oxidase 1 gene have
been used successfully in species identification.
There are numerous examples of species identification in forensic science: these
include the identification of tiger DNA within traditional medicines [7]; protected
bear species in bear bile products [8]; rhino DNA smuggled as bovine bone [9];
turtles as food products and as shell ornaments [10]; identification of elephant ivory
within statues [11]; protected shark species collected for shark fin soup [12, 13]; the
identification of the Tibetan antelope on woven shawls [14]; and the identification
of cannabis from seeds [15].
In green plants, loci on the chloroplast DNA are used more commonly for species
identification. The loci include matK and trnH - psbA [16], the transfer RNA (tRNA)
genes [17], the internal transcribed spacer (ITS) regions in ribosomal RNA (rRNA)
[18, 19] and genes such as ribulose 1,5 bis-phosphate carboxylase ( rbcL ), ATP syn-
thase beta ( atpB ) and the NADH dehydrogenase subunit 5 ( ndhF ) [20]. In the case
of the rbcL locus over 6500 plant species have so far been examined. Although this
is a large number, it represents a fraction of the actual plant species known. The
complexity of genomes within the plant kingdom reflects the large number of loci
used in species identification.
Linkage to an individual using STR loci
Plants and animals contain STRs, similar to those described in Chapter 6. The
human STR loci were identified and characterized as they are often intron based
and were discovered while examining the gene sequences. Although all animal and
plant species contain STRs, they have only been characterized to any great extent in
commercially important species such as dog [21 - 23], cat [24 - 26], horse [27, 28],
cow [29], pigeons [30], pine trees [31, 32] and cannabis [33 - 36]. STR loci are only
useful if there is a database of alleles for comparison. There are databases in place for
the species listed above. Originally the STR loci identified were predominantly din-
ucleotide repeats, but with the increasing knowledge of the genomes of domesticated
species, tetranucleotide repeats are more common.
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