The orientation of gene maps by recombination of flanking markers for the am locus of Neurospora crassa

Fincham (1967), Smyth (1973b) and Rambosek and Kinsey (1983) have each generated fine-structure maps of the am gene of Neurospora crassa. Each map had a consistent linear order of alleles but the assignment of an orientation with respect to other linkage group-V loci differed. Fincham found the end marked by the am ₆ allele to be at the distal end of the locus, Smyth found am ₆ to be at the proximal end while the data of Rambosek and Kinsey did not suggest an orientation. Smyth's orientation has been adopted as the standard, but not unreservedly. We have aligned the genetic and physical maps of the am gene, showing that am ₆ is at the distal end, supporting Fincham's orientation. However, we suggest that an assumption used to orient fine structure genetic maps is flawed and that the conflicting orientation between these three studies follows from the different choice of flanking markers.