Characteristics of gene conversion and Rec factor of the i locus of Sordaria fimicola.

Abstract

Apart from the previously studied g-locus, the i-locus showed the following chracteristics. (A) 1-point cross conversion frequencies were roughly constant around 10 .times. 10-3, unless associated with a Rec+ factor. (B) The interallelic conversion frequencies were either the sum of parental 1-point cross conversion frequencies (20 .times. 10-3) or still higher than this, suggesting that this locus has compound composition with at least 2 units. (C) Whenever interallelic cross conversion frequency was notably higher than 20 .times. 10-3, the ascus frequency of the spore color ratio, 2+, 2i, 4b (asci of this composition can be developed through gene conversion or appear as tetratypes through reciprocal recombination) was high enough to include the excess portion of the conversion frequency, leaving substantial surplus. This suggests that the i-locus is composed of multiple units, and, at the joints of units, ordinary reciprocal cross-overs occur producing tetratype asci, consequently raising the apparent conversion frequencies. (D) The original blu6 allele was accompanied with a Rec+ factor and, therefore, its conversion frequency was low. Through gene conversion, this factor was removed from blu6 and transferred to the wild-type allele. (E) The Rec factor functions as a mutator on the alleles in the i-locus and, by itself, it was labile. Among the above characteristics, C and E, respectively, show close relationships with the compound genes of Neurospora and the mutable genes of Zea.