Physical mapping of chromosome 21.

Chromosome 21, the smallest human chromosome, has been the subject of intense study because it is the chromosome which, when present in an extra copy, leads to Down Syndrome. Moreover, there are genes important for several human genetic disorders on this chromosome, and a significant number of individuals with aneuploidies of regions of the chromosome have been identified. A high fidelity, high resolution physical map of chromosome 21 will be of immense value in generating an accurate genotype/phenotype map of the chromosome and in identifying and isolating genes on the chromosome which may be responsible for various human genetic disorders. Here we describe the current status of our attempts to create such a map. This includes attempts to integrate various physical mapping approaches. Progress towards construction of a minimal set of yeast artificial chromosomes (YACs) spanning the chromosome is described.