GENETICS OF SORDARIA FIMICOLA. V. ABERRANT SEGREGATION AT THE G LOCUS

K itani , Y., L. S. O live , and A rif S. E l ‐A ni . (Columbia U., New York City.) Genetics of Sordaria fimicola. V. Aberrant segregation at the g locus. Amer. Jour. Bot. 49(7): 697–706. Illus. 1962.—Aberrant segregation of the gray‐spore color locus in Sordaria fimicola was studied with the aid of closely linked markers. It was found that 6:2 and 5:3 asci occur with about the same frequency, but asci with an excess of wild‐type spores occur with a frequency 5.5 times that of asci with an excess of gray spores. Also, the frequency of related crossing over (occurring close to the miscopied loeus and involving the miscopying strand) was much higher than the expected value, and in 5:3 asci it appears to be at least twice that found in 6:2 asci. Nine aberrant 4:4 asci, each with 2 spore pairs heterogeneous for color, were found. These are believed to have resulted from reciprocal double transreplication. The rarest aberrant type was represented by a single 7:1 ascus, which is difficult to explain on the basis of a single meiotic process. Miscopying is discussed with relation to an 8‐strand model of paired homologues and the occurrence of localized chromosome pairing during prezygotene DNA synthesis. Several possible explanations for the occurrence of aberrant tetrads are considered. Miscopying has also been found to involve several spore‐color loci not previously studied; whereas, several other such mutant loci fail to show evidence of it. One locus ( m ) shows abnormal segregation of the 6:2 but not the 5:3 type.