Analysis of conversion tracts associated with recombination events at the am locus of Neurospora crassa

In cross B163, heteroallelic am ¹ am ⁶ and heterozygous for both conventional genetic flanking markers and closer molecular markers, we previously found that the majority on flanker exchanges were remote from events that generated prototrophic recombinants. We report here that natural polymorphisms distinguishing the parents of cross B163 also include sequences within and closely flanking am. Segregation of these markers in B163 prototrophs confirms that the majority of meiotic recombination events at am resulted from gene conversion. Conversion of am ⁶, the distal allele, is more frequent than conversion of am ¹. Twelve percent of tracts in am ⁶ convertants were discontinuous while 30% of continuous tracts converting am ⁶ extend less than 741 bp. Received: 8 September 1997 / 15 April 1998