The UniGene set, compiled from all gene sequences in GenBank that have a bona fide 3' untranslated region, contains 3125 sequences. As the number of ESTs grows, assessing the accrual rate of new sequences and developing strategies for finding unrepresented expressed sequences are important. Building the Gene Map Building a complete gene map requires information integration from different mapping approaches. This year has seen a large increase in the number of ESTs and other markers mapped to the highest-resolution levels. This is part of a larger project in which 10,000 chromosomally assigned STSs have been screened against the YAC library, giving an average marker spacing of 300 kb.
Pilot experiments are under way to compare and integrate the map with RH maps.
In general, good concordance exists among genetic, RH, and YAC maps. Two sets of RHs are being used to construct framework maps with a resolution of around 500 kb that can be used to locate unknown ESTs. The Stanford hybrids are generated with a higher dose of X rays and have about twice as many breaks, thus allowing mapping at higher resolution, but the Cambridge-G n thon set allows significant linkage to be obtained with a higher fraction of cDNAs. ESTs are proving to be a source of useful genetic markers that can be linked explicitly to the genetic map. As the gene map is built up, it will provide reagents and information that can be applied to genome sequencing.