Further studies of linkage and mappings of the loci of genes in group 3 on chromosome 1 of the domestic fowl.

1. Evidence is presented to confirm the placing of the extended black E-locus in linkage Group 3 on chromosome 1, E being linked with peacomb P by 43 map units. P has been shown to be linked with dark-brown columbian Db and sleepy-eye se by 32 and 45 map units, respectively, se being independent of E. 2. Evidence is also presented to demonstrate independence of E and Db; hence, Db and se have their loci on the same side of P, the gene order being E-P-Db-se, thus contradicting published mappings which place P between Db and se. 3. An investigation into the deductive relationships on which published mappings are based led to the conclusion that insufficient evidence existed for the inclusion of the sub-group comprising blood group Ea-P, naked neck Na, silky feathering h and flightless Fl as part of Group 3. 4. Furthermore, it appears only 4 genes in Group 3 have actually had their loci mapped; blue egg O, P, the eumelanin extension charcoal cha and the feather growth restrictor tardy t. 5. No evidence appears to have been presented to establish on which arm of chromosome 1 any of the other genes in Group 3 have their loci. A revised map of chromosome 1 and a schematic arrangement to demonstrate the relative linkage distances of the loci of the unmapped genes in Group 3 are presented and explained.