Alleles of the Hotspot cog Are Codominant in Effect on Recombination in the his-3 Region of Neurospora

Abstract

There are two naturally occurring functional alleles of the recombination hotspot cog, which is located 3.5 kb from the his-3 locus of Neurospora crassa. The presence of the cog ϩ allele in a cross significantly increases recombination in the his-3 region compared to a cross homozygous for the cog allele. Data obtained shortly after discovery of cog ϩ suggested that it was fully dominant to cog. However, a dominant cog ϩ conflicts with observations of hotspots in Saccharomyces cerevisiae and Schizosaccharomyces pombe, in which recombination is initiated independently of homolog interactions, and suggests recombination mechanisms may differ in Neurospora and yeast. We present evidence that cog alleles are codominant in effect on both allelic recombination in his-3 and crossing over between loci flanking his-3. In addition, we show that genetic background variation has at least a twofold effect on allelic recombination. We speculate that variation in genetic background, together with the complexities of recombination in crosses bearing close mutant alleles, accounts for the previous conclusion that cog ϩ is dominant to cog.

Quantitative Trait Loci (QTL) Analysis For Rice Grain Width and Fine Mapping of an Identified QTL Allele gw-5 in a Recombination Hotspot Region on Chromosome 5

“…This novel finding creates an opportunity, as well as poses a challenge, for molecular geneticists in the further exploration of the relationship between fine structure and crossover frequency of rice chromosomes by dissecting the mechanism of high recombination frequencies in the four regions surrounding the gw-5 gene between the two parents (Asominori and CSSL28). Similarly, linkage mapping strategies have been used to investigate the recombination hotspots on chromosomes of a wide variety of organisms, e.g., wheat (Faris et al 2000), neurospora (Yeadon et al 2004), mouse (Kelmenson et al 2005), and human (Minin et al 2007). …”

Rapid genetic mapping in Neurospora crassa

“…In contrast, the genetic lengths of the left arm of Linkage group II and distal segments of the right arms of Linkage Groups II, VI and VII were all greater than the expected values. The presence of recombination hotspots and the nonrandom distribution of recombination events in general have been well documented in N. crassa (Bowring and Catcheside, 1999b;Catcheside, 1981;Catcheside, 1975), and attributed to modulators of recombination that include rec genes, cog and spo11 (Angel et al, 1970;Bowring et al, 2006;Catcheside, 1981;Yeadon et al, 2004). Allelic differences in these genes may also contribute to the distribution of recombination events that we detected.…”

“…Thus it will be possible to investigate the effect of specific mutations on recombination and/or its control and to test whether the effects are global or localized to distinct chromosomal regions. Interesting candidates would include those genes previously identified through classical and related molecular approaches to modulate recombination (Angel et al, 1970;Bowring et al, 2006;Catcheside, 1981;Kato et al, 2004;Suzuki et al, 2005;Yeadon et al, 2004). Similarly, one could quantitatively assess chiasma interference at a genome-wide level (Bowring and Catcheside, 1999a;Foss et al, 1993).…”

Discrepancies Between Recombination Frequencies and Physical Distances in Aspergillus nidulans: Implications for Gene Identification

“…For brevity we give a few examples from fungi but the factors involved affect recombination frequencies across a wide range of organisms. Such factors include environmental influences such as nutritional state (e.g., Abdullah and Borts 2001), genetic factors including both trans-acting genes (e.g., Catcheside 1981; Yeadon et al 2004) and cis-acting recombination hotspots (e.g., Pryce et al 2005;Steiner and Smith 2005), and the long-known effects of chromosomal rearrangements (reviewed by Käfer 1977 andPerkins 1997). These effects can be considerable.…”