Fig. 1. Positional cloning of the hab locus. (A) Genetic map of the hab locus near the centromere (filled circle) of Linkage Group 7, showing the positions of the microsatellite (Z) markers and the number of recombinants between each marker. (B) The chromosomal walk was initiated at flanking markers Z20715 and Z8156, which were used to probe PAC and BAC large insert genomic libraries. Clones are numbered according to reference number (see Materials and methods). The critical region of 150 kb that contains hab was defined by the two closest recombination events. Sequencing of this region, as part of the Zebrafish Genome Project (Sanger Institute), revealed a number of candidate genes, including the zebrafish homolog of E-cadherin.