ANALYSIS OF PERICENTROMERIC CHROMOSOME-21 SPECIFIC YAC CLONES BY FISH- IDENTIFICATION OF NEW MARKERS FOR MOLECULAR-CYTOGENETIC APPLICATION

Fluorescence in situ hybridization (FISH) of chromosome 21 specific ye ast artificial chromosome (YAC) clones after Alu-PCR (polymerase chain reaction) amplification has been used to find new region-specific DNA probes for the heterochromatic region of chromosome 21. Six overlappi ng YAC clones from a pericentromeric contig map (region 21cen-21q11) w ere analyzed. Four YAC clones were characterized as hybridizing to sev eral chromosomal locations. They are, therefore, either chimeric or sh ared by different chromosomes. Two of them containing alphoid satellit e DNA, are localized at the centromeric regions of chromosomes 13 and 21 (clone 243A11), and on 13cen, 21cen and 1q3 (clone 781G5); the two others are localized at both 21q11 and 13q2 (clone 759D3), and at 18p (clone 770B3). Two YACs were strongly specific for chromosome 21qll on ly (clones 124A7 and 881D2). These YACs were used effectively as probe s for identifications of chromosome 21 during metaphase and interphase analysis of 12 individuals, including three families with Down syndro me offspring, and 6 amniocyte samples. The location of YAC clones on 2 1q11 close to the centromeric region allows the application of these c lones as molecular probes for the analysis of marker chromosomes with partial deletions of the long arm as well as for pre- and postnatal di agnosis of trisomy 21 when alphoid or more distal region-specific DNA probes are uninformative. Overlapping YAC clones covering human chromo some 21q may be systematically used to detect a set of band-specific D NA probes for molecular-cytogenetic application.