Strategy

In making a chromosome-specific or regional HAPPY map, the mapping panel itself represents the whole genome. Therefore, it is the markers which need to be specific to the chromosome or region to be mapped.

For human chromosome 14, marker sequences were obtained mainly from hybrid cell-lines carrying human chromosome 14 in a rodent cell background, and also from flow-sorted human chromosomes.

A total of 1001 chromosome-14 markers were successfully typed on a mapping panel prepared from normal human DNA, containing fragments of around 1-2Mb. This yielded several linkage groups, separated by unlinked gaps where consecutive markers lay more than about 1Mb apart.

To order and orientate these linkage groups, longer-range mapping panels (containing larger fragments) were prepared. A small subset of the markers (chiefly those lying at the ends of the linkage groups) were typed on these long-range panels, bridging the gaps and allowing a map of the complete chromosome to be assembled.

Some time after the publication of this map, the completion of the sequence of human chromosome 14 (the first human chromosome to be sequenced without gaps) made it possible to compare our map retrospectively with the published sequence. The comparison showed that the HAPPY map was the most accurate map produced of a human chromosome.