Recombination Mechanisms at the pan-2 Locus in Neurospora crassa*

The nature of the mechanisms responsible for recombination between closely linked, functionally similar mutants has become of increasing signifi-cance in recent genetic investigations. Much evi-dence now indicates that crosses between such mutants may exhibit behavior unexpected on the classical theory of recombination, which involves reciprocal crossing over at the four strand stage of meiosis accompanied by positive chromosome interference. This evidence, which is now avail-able in a variety of microorganisms, came initially from the observation that prototrophs recovered in random ascospore platings from crosses of ap-parently allelic auxotrophic mutants having closely linked markers on either side of the locu