D12S67, a bipartite locus: differential amplification of parts of the nucleotide sequence reveals considerable polymorphism.

The STR system D12S67 was amplified by polymerase chain reaction (PCR) and analyzed by denaturing gel electrophoresis followed by silver staining. Among 133 DNA samples from Japanese individuals, 11 alleles were observed and the heterozygosity was 80%. When sequences of the alleles were compared, each allelic segment contained 35-45 gata or gaca tetranucleotide repeats. Although a (gaca)n repeat block was concentrated in a defined region, nine different blocks of (gata)n repeats were observed separated by the (gaca)n repeat and single copy sequences. In addition, the allelic differences result from the total number of repeats of at least three (gata)n and the (gaca)n repeat regions. Novel primers overlapping part of the sequence with each other were constructed in the center of the D12S67 sequence, and the 5' and 3' segments were amplified by PCR. Both of these segments were highly polymorphic and showed heterozygosities of 77 and 78% with 7 and 10 alleles, respectively. The genotypes of the two polymorphisms were not concordant with the original polymorphism and the combination of the 5' and 3' side segment polymorphisms enabled further detailed classification of the D12S67 locus by simple comparison of the PCR product sizes. The number of the allele types increased up to 35 and the heterozygosity to 93%.