Biology Reference
In-Depth Information
The first case that highlighted the use of animal STR typing was that of Snowball
the cat. In this case a bloodstained jacket was found next to the body of a female.
White hairs were noted on the jacket and identified as being from a cat. The
estranged husband of the deceased denied any knowledge of the jacket, but a white
cat called Snowball shared the home where the husband stayed. Ten feline STRs
were tested on a sample from Snowball and the hair from the jacket and found to
match. Population studies on nearby cats indicated a high power of discrimination
using these 10 STR loci and led to the conviction of the husband [37]. Since then
there have been cases of dog STR typing, to link dog hairs to a living dog [38].
These types of analyses are used to link a non-human DNA to an investigation of
an alleged crime against a person.
Crimes against animals include badger baiting, where dogs are set on wild badgers.
STR loci have been developed to link badger blood and hairs from items retrieved
from anyone alleged to have been present at such an act to a deceased badger [39].
Other uses of STR typing are to link offspring of birds of prey to the hen and cock
bird, as it is permissible to own a bird if bred from captive pairs rather than taken
from the wild [40, 41]. If a person claims that a bird of prey in their possession was
bred from captive stock, then this can be tested.
Botanical uses of STR typing include the linkage of leaf material within a car
to an oak tree growing at the site of a shallow grave [42]. In this case four oak
STR loci were found to match between the leaf and reference material from the tree,
with a match probability of 2.06
10
−
6
. Many more such botanical cases could be
performed if there were more comprehensive reference databases available.
Adjustment of allele frequencies from human DNA databases was discussed in
Chapter 8. The same process should be undertaken with non-human STR data. Rare
or absent alleles need to be accounted for either by the application of a minimal
allele frequency, or the addition of the unknown and known alleles to the database
followed by a recalculation. Kinship factors can be a problem with breeds, or where
there are very small populations remaining and species that reproduce colonially.
In these cases a knowledge of the biology of the species is needed such that an
appropriate kinship factor is applied to the alleles when determining the overall
genotype frequency.
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Linkage to an individual using mitochondrial loci
Non-human material is often a fine animal hair, in which case there is insufficient
genetic material to obtain an STR profile. Examination of the control region of
the mitochondrial DNA can be conducted in much the same way as the sequence
comparison of HVI and HVII as described for human linkage. Mitochondrial control
databases exist for dog [43 - 45] to allow an estimate of the chance that another dog
might have the same DNA type. The power of discrimination will be less using
mitochondrial sequence data than using STR analysis; however, these data can still
be of value as associative evidence.
