Recombination events that span sites within neighbouring gene loci of Neurospora

SUMMARYEvidence is given that me-7 and me-9 are separate but contiguous gene loci.The pattern of polarized recombination throughout the me-7 me-9 region indicates the location of a recombinational discontinuity between the known me-7 alleles and the known me-9 alleles.Recombination events may include sites in both genes but such events are not preferentially associated with parental combinations of flanking markers.Recombination events extending into both genes provide an extra criterion for the ordering of the sites within the me-7 locus. The order so obtained confirms that deduced from the flanking markers of me+ recombinants from me-7 × me-7 crosses.In me-7 × me-9 crosses but not in me-7 × me-7 crosses, the map order derived on the assumption that single exchanges are more frequent than apparent triple exchanges is the reverse of that derived from prototroph frequencies. It is concluded that the former criterion is more likely to have provided the correct order and the anomalous prototroph frequencies reflect the polarity of gene conversion within me-7.