Segregation analysis of tetra- and pentanucleotide short tandem repeat polymorphisms: deviation from Mendelian...

Short tandem repeat (STR) polymorphisms are powerful tools for linkage studies, chromosome mapping and population analysis. The instability of these microsatellite regions is a prevailing event in several tumors and human genetic diseases and, despite various reports associating instability-related genes and meiosis control, the dynamics of these STR regions in normal cells/individuals has frequently been disregarded. Having previously assayed somatic instability in gastric cancer for some tetra- and pentanucleotide STRs and given the increased application of this type of marker for routine forensic expertise, we report the results of an extensive analysis of segregation in nuclear families of a normal population for the same loci. No mutations were detected in 2374 parent/offspring allelic transfers at TH01, TPO, VWA31/A, MBPB, and CD4 STR loci. Nonsignificant differences were found between gene frequencies of parental and offspring generations. However, the segregation analysis revealed significant deviation from Mendelian expectations for: VWA31/A locus - alleles 19, 17 and 14 and TH01 locus - allele 6. In particular, parental meiosis strongly favored specific allele transmission, depending upon the sex of the offspring. Specific mating types are apparently responsible for most of these abnormal segregations. These results suggest selective factors working either at the gametic or zygotic levels.