Partial physical map of human chromosome 21.

The long arm of human chromosome 21 has been analyzed with unique sequence DNA probes, using an expanded panel of somatic cell hybrids containing defined regions of the chromosome, and both standard and pulsed field gel electrophoresis. Each member of the hybrid cell panel contains either a normal chromosome 21, or one of 11 different translocations or deletions within the long arm. Together, these now include 11 breakpoints, defining 11 long arm regions. Thirty-two unique sequence probes have been localized to these regions by standard gel electrophoresis. Analysis by pulsed field gels indicates that 27 of these identify a total of 18 Not1 restriction fragments, which together account for approximately 17 million base pairs, over half the long arm. Five physical linkage groups have been identified, as well as patterns in the distribution of unique sequences and GC-rich chromosomal regions. This information can be correlated with that obtained by other methods and contributes to the construction of a detailed physical map of this chromosome.