Biomedical Engineering Reference
In-Depth Information
Table 14.2
Classification of satellite
DNA.
Degree of repetition
Repeat-unit
Type of repeat
per locus
Number of loci
length (bp)
Satellite
10
3
-10
7
One to two
1000-3000
per chromosome
Minisatellite
10-10
3
Thousands per
9-100
genome
Microsatellite
10-10
2
Up to 10
5
1-6
per genome
H1
H1
A
G G A G G T G G G C A G G A G G
Core sequence
Individual
A
Probe 33.6
[(A G G G C T G G A G G )
3
]
18
Probe 33.15
(A G A G G T G G G C A G G T G G)
29
C
(G G G A G T G G G C A G G A G G)
14
Probe 33.5
Individual
B
Fig. 14.7
Probes used for DNA fingerprinting.
Multilocus probes can also be used to prove or
disprove paternity and a unique example, which
was part of an immigration test case, is shown in
Box 14.1. The technique also has application in
many other areas, such as pedigree analysis in cats
and dogs ( Jeffreys & Morton 1987), confirming
cell-line authenticity in animal cell cultures (Devor
et al.
1988, Stacey
et al.
1992) and monitoring the
behaviour and breeding success of bird populations
(Burke & Bruford 1987).
In criminal cases, a major disadvantage of multi-
locus probes is the complexity of the DNA fingerprint
provided. Showing innocence is easy, but proving
identity is fraught with problems. The issue boils
down to calculations of the probability that two
profiles match by chance as opposed to having come
from the same person (Lewontin & Hartl 1991). For
this reason forensic scientists have moved to the use
of single-locus probes and an example is shown in
Fig. 14.8. The latest variation of the technique,
introduced in the UK in 1999, targets 10 distinct
loci, and the likelihood of two people sharing the
same profile is less than one in a billion (thousand
million). Chance matches are even less likely in the
USA, where the FBI routinely examines 13 VNTR
loci. Another advantage of single-locus probes is
Individual
C
Individual
A
Individual
B
Individual
C
Fig. 14.6
Restriction fragment length polymorphisms
caused by a variable number of tandem repeats between
the two
HinfI
restriction sites. The upper part of the diagram
shows the DNA structure for three different individuals.
The lower part of the diagram shows the pattern obtained on
electrophoresis of
HinfI
cut DNA from the three individuals
after hybridization with a probe complementary to the
sequence shown in pink.
year, DNA-fingerprinting evidence was used in the
USA. It is worth noting that DNA evidence has been
used to prove innocence as well as guilt (Gill &
Werrett 1987).
