Mapping the mouse craniofacial mutation first arch (Far) to chromosome 2.

First arch (Far) is a semidominant mutation that causes severe craniofacial defects in mice. Here we report the results of linkage studies with the chromosome 2 markers nonagouti, pallid, and Ulnaless. Far is loosely linked to nonagouti (24-37 cM), more closely linked to pallid (13-28 cM), and closely linked to Ulnaless (2.3 +/- 1.5 cM). The embryological defect in Far mutants is confined to one segmentally-derived region of the head, the anterior first branchial arch. It may therefore be significant that, in mapping near Ulnaless, Far also maps in the vicinity of the Hox-4 gene cluster.