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TABLE 2.1  Genetic Markers Used in Forensic Identification

Nature of Variation at Locus

Locus Example

Method of Detection

Number of Alleles

Diversitya

Variable Number Tandem Repeat (VNTR)b

D2S44 (core repeat 31 bp)

Intact DNA digested with restriction enzyme, producing fragments that are separated by gel electrophoresis; alleles detected by Southern blotting followed by probing with locus-specific radioactive or chemiluminescent probe

At least 75 (size range 700-8500 bp); allele size distribution continuous

ca. 95% in all populations studied

DIS80 (core repeat 16 bp)

Amplification of allelic sequences by PCR; discrete allelic products separated by electrophoresis and visualized directly

ca. 30 (size range 350-1000 bp); alleles can be discretely distinguished

80-90%, depending on population

Short Tandem Repeat (STR)c

HUMTHO 1 (tetranucleotide repeat)

Amplification of allelic sequences by PCR; discrete allelic products separated by electrophoresis on sequencing gels and visualized directly

8 (size range 179203 bp); alleles can be discretely distinguished

70-85%, depending on population

Simple Sequence Variation d

DQA (an expressed gene in the histocompatibility complex)

Amplification of allelic sequences by PCR; discrete alleles detected by sequence-specific probes

8 (6 used in DQA kit)

85-95%, depending on population

Polymarker (a set of 5 loci)

Amplification of allelic sequences by PCR; discrete alleles detected by sequencespecific probes

Loci are bi- or triallelic; 972 genotypic combinations

37-65%, depending on locus and population

Mitochondrial DNA Control Region (Dloop)

Amplification of control-region sequence and sequence determination

Hundreds of sequence variants known

Greater than 95%

aIn a randomly mating diploid population, diversity is the same as heterozygosity. In general, including haploid mitochondria, the value is 1 - Sipi2 (for explanation, see Chapter 4).

bVNTR loci contain repeated core sequence elements, typically 15-35 bp in length. Alleles differ in number of repeats and are differentiated on the basis of size.

c STR loci are like VNTR loci except that the repeated core sequence elements are 2-6 bp in length. Alleles differ in number of repeats and are differentiated on the basis of size.

d Nucleotide substitution in a defined segment of a sequence.



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