Recombination events that span sites within neighbouring gene loci ofNeurospora

Abstract

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.

The Inducible Quinate-Shikimate Catabolic Pathway in Neurospora crassa: Genetic Organization

“…Evidence has suggested that the extent of genetic heterogeneity affects the frequency of gene conversion (Fogel, Hurst & Mortimer, 1971). Determination of gene order from segregation of the unselected qa marker is complicated by the fact that approximately 75 % of the methionine prototrophs result from gene conversion ; furthermore, these conversion frequencies exhibit a marked polarity pattern (Murray, 1970). In view of this consideration, the results in Table 6 are consistent with a genetic map in which both qa-3 and qa-4 are located to the left of me-?.…”

“…Crosses with me-9. Murray (1970) has shown that me-9 is adjacent to, and to the right of, me-7 in L.G. VII.…”

Genetic Order of the Galactose Structural Genes in Saccharomyces cerevisiae

“…In addition to establishing a probable order for the galactose structural genes, the data presented in Tables 1 and 2 indicate that both mitotic and meiotic co-conversions are able to span a genetic length extending into at least three adjacent genes. Meiotic co-conversions involving sites in two adjacent genes have been reported previously (2, 7).…”

Multiple recombinational events within the84 Wlocus ofAscorolus immersus

“…Recently Fogel, Hurst & Mortimer (1970), using point mutations within arg4 locus of Saccharomyces cerevisiae, demonstrated that the frequency of simultaneous conversions correlates with the physical distance between mutant sites. Demonstration of simultaneous conversions involving sites from neighbouring cistrons (Case & Giles, 1964;Paszewski, 1967;Putrament, 1967;Murray, 1970;Toure & Marcou, 1970) suggests that conversion is a type of recombination observed in recombination studies within short segments of genetic material, but not necessarily coinciding with genes. The second feature of gene conversion is its high fidelity.…”