Abstract
LATE-PCR, an advanced form of asymmetric PCR amplification developed in the Wangh laboratory, offers a novel approach to construction of a clinically-compatible. convenient, reliable and sensitive assay for detection of Down's syndrome, a genetic condition caused by trisomy of chromosome 21. The assay described in this thesis interrogates genetic markers in chromosome 21 to distinguish between diploid genomes having two copies of chromosome 21 and triploid genomes having three copies of the same chromosome. These genetic markers, also known as heterozygous markers or alleles. are comprised of single nucleotide polymorphisms (SNPs) that differ in the paternal and maternal copies of chromosome 21. To increase the likelihood of finding a heterozygous (i.e. informative) SNP marker I developed LATE-PCR assays for a set of high frequency SNP sites within a region of chromosome 21 that is tightly linked to Down's syndrome. Starting with samples containing as little as a single cell. the assay can amplify as little as a single SNP and then can analyze the SNP using a single fluorescent probe at several temperatures, in order to establish the fraction of chromosome 21 copies that have one SNP sequence among the total number of chromosome 21 copies in the sample. For instance, the normal diploid genome of a heterozygous individual has two copies of chromosome 21, either one of which (50%) has its own SNP variant. In individuals with trisomy chromosome 21, one of the variants at a heterozygous SNP will be present in either 66% or 33% of all copies of that SNP on all copies of chromosome 21. Utilization of SNPs with a high frequency of heterozygosity in the European and global populations to ensure a 98.5% chance of obtaining at least two informative SNPs for every subject.