Recombination within theamgene ofNeurospora crassa

Abstract

Maps have been made showing the order ofammutant sites using (a) frequencies ofam+recombinants from crosses betweenammutants and (b) the modes of distribution of theam+recombinants among the two parental and two recombinant classes with respect to the flanking markersinosandsp.It is possible to arrange the sites in an order such that, in almost all the crosses yielding useful numbers ofam+recombinants, thespallele originally in coupling with the distalammutant site occurs in the majority of the recombinants. No such consistent pattern was found with respect to theinosmarker. The order obtained by reference tospagreed with the best order deducible from recombination frequencies.The data are consistent with the hypothesis thatam+recombinants arise by a process of gene conversion, that there is a gradient of conversion frequencies from the right (inosor distal) end of the gene to the left (spor proximal) end, and that conversion tends to be associated (though less than 50% of the time) with crossing-over, especially on the distal side.There is no obvious relationship between the map position of a givenammutant and the properties of the protein product of the mutant gene.