Box DNA profiling

The loci used for human DNA profiling are a general class of DNA sequence marker known as simple tandem repeat (STR), simple sequence repeat (SSR), or microsatellite loci. These loci feature tandemly repeated DNA sequences of one to six base pairs (bp) and often exhibit many alleles per locus and high levels of heterozygosity. Allelic states are simply the number of repeats present at the locus, which can be determined by electrophoresis of PCR amplified DNA fragments. STR loci used in human DNA profiling generally exhibit Hardy-Weinberg expected genotype frequencies, there is evidence that the genotypes are selectively "neutral" (i.e. not affected by natural selection), and the loci meet the other assumptions of Hardy-Weinberg. STR loci are employed widely in population genetic studies and in genetic mapping (see reviews by Goldstein & Pollock 1997; McDonald & Potts 1997).

This is an example of the DNA sequence found at a microsatellite locus. This sequence is the 24.1 allele from the FGA locus (Genbank accession no. AY749636; see Fig. 2.8). The integral repeat is the 4 bp sequence CTTT and most alleles have sequences that differ by some number of full CTTT repeats. However, there are exceptions where alleles have sequences with partial repeats or stutters in the repeat pattern, for example the TTTCT and CTC sequences imbedded in the perfect CTTT repeats. In this case, the 24.1 allele is 1 bp longer than the 24 allele sequence. (continued )

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