D20S16 IS A COMPLEX INTERSPERSED REPEATED SEQUENCE - GENETIC AND PHYSICAL ANALYSIS OF THE LOCUS

The genomic structure of the D20S16 locus has been evaluated using gen etic and physical methods. D20S16, originally detected with the probe CRI-L1214, is a highly informative, complex restriction fragment lengt h polymorphism consisting of two separate allelic systems. The allelic systems have the characteristics of conventional VNTR polymorphisms a nd are separated by recombination (theta = 0.02, Z(max) = 74.82), as d emonstrated in family studies. Most of these recombination events are meiotic crossovers and are maternal in origin, but two, including dele tion of the locus in a cell line from a CEPH family member, occur with out evidence for exchange of flanking markers. DNA sequence analysis s uggests that the basis of the polymorphism is variable numbers of a 98 -bp sequence tandemly repeated with 87 to 90% sequence similarity betw een repeats. The 98-bp repeat is a dimer of 49 bp sequence with 45 to 98% identity between the elements. In addition, nonpolymorphic genomic sequences adjacent to the polymorphic 98-bp repeat tracts are also re peated but are not polymorphic, i.e., show no individual to individual variation. Restriction enzyme mapping of cosmids containing the CRI-L 1214 sequence suggests that there are multiple interspersed repeats of the CRI-L1214 sequence on chromosome 20. The results of dual-color fl uorescence in situ hybridization experiments with interphase nuclei ar e also consistent with multiple repeats of an interspersed sequence on chromosome 20. (C) 1995 Academic Press, Inc.