CDNA SELECTION FROM 10 MB OF CHROMOSOME-21 DNA - EFFICIENCY IN TRANSCRIPTIONAL MAPPING AND REFLECTIONS OF GENOME ORGANIZATION

The technique of cDNA hybridization selection has been applied individ ually to 16 YAC clones mapping to various regions of the long arm of h uman chromosome 21. YACs represented similar to 10 Mb of non-overlappi ng DNA, and cDNA sources included fetal brain, whole fetus, and adult testes, thymus, liver and spleen. Sequencing, Northern analysis, RT-PC R and cDNA library screenings have been used to identify and partially characterize a non-redundant set of novel genes. A preliminary analys is strategy of the selected cDNAs has proven rapid and effective for i solation of the more highly represented genes and is suitable for surv ey transcriptional mapping efforts. By scaling up to screen >1000 cDNA fragments per 100 kb of YAC DNA, more rare transcripts are identified and lead to comprehensive gene maps. Strong regional variations in tr anscriptional activity were observed, with gene densities ranging from <1/2000 kb to >1/15 kb. This effort has produced a large number of ne w genes of potential relevance to Down Syndrome.