New equations and a method for finding nine parameter values for two alleles at one locus to study gene conversion using Ascobolus immersus

Abstract

A quantitative treatment is given for meiotic gene conversion with its parameters and equations for their interactions to determine allele segregation class frequencies from heterozygotes. The possible pairing of both pairs of nonsister chromatids in a bivalent at exactly the same point is included. Using sets of data from Ascobolus immersus, it is shown that values for all nine parameters for hybrid DNA models of recombination can be obtained using an iterative computer program. The accuracy of the values is estimated and the double-strand gap repair model is considered. The parameter values obtained invalidate most of the simplifications used in previous quantitative analyses of gene conversion data. They showed total bias in strand preference in asymmetric hybrid DNA formation and some bias in which type of chromatid is the invading one. There were slight differences in repair frequency between the two types of mispair and very large differences in the direction of repair. Conversion control factors had major effects on hybrid DNA formation and repair of mispairs.

The nine-parameter gene conversion model: simpler equations, validity tests, and multiple fits

“…One can use the half-octad formulae in Table 2 (a) to test Fincham's predictions, using the calculated halfoctad figures he quoted from Lamb and Zwolinski (1992) Table 3, set 3, trying various arbitrary values for one or two particular parameters to see if one can still get valid values (0.0 to plus 1.0, inclusive) for the remaining parameters. The validity of the LambZwolinski model has also been tested directly using the 'set-and-find' method described in the Abstract and Results.…”

“…From Table 3 of Lamb and Zwolinski (1992), data set 3, one can use the nine parameter values given to calculate--from the half-octad formulae given in Table 2 (a) in this paper--that half-octad frequencies in those data were: 4:0, a = 0.420; 3:1, b = 0.174; aberrant 2:2, c = 0.015; 1:3, d = 0.095; 0:4, e = 0.144; correction 2:2,f= 0.152; total, 1.000. Fincham's (1994) prediction was that: 'Any set of values for Lamb and Zwolinski's seven molecular parameters that generate these five numbers would satisfy the data equally well.…”

“…Their scheme included symmetric and asymmetric hybrid-DNA (hDNA), as in the Meselson and Radding (1975) model, although it is not tied to the particular details of that model. The relevance of double-strand gap-repair as a source of gene conversion in such fungi as Ascobolus was assessed by Lamb (1987), with a quantitative treatment by Lamb and Zwolinski (1992).…”

“…For studies of gene conversion and crossing-over mechanisms, it is important to be able to determine those parameter values. For example, Lamb and Zwolinski (1992) found from Ascobolus immersus data that ~ was always zero; that is, it was always the same strand of DNA that was the invader in asymmetric hybrid DNA. Such findings about parameters help evaluate different recombination models.…”

Gene conversion disparity in yeast:its extent, multiple origins, and effects onallele frequencies

“…Unless strand invasion parameter = 0.5, this disparity increases as correction frequency p differs from q; unless p = q, this disparity increases as departs from (1 ). The evidence from Ascobolus (Lamb & Zwolinski, 1992) for w1 is for extreme strand invasion disparity, with = 0.0 or 1.0. If = (1 ) and/or p = q, 5:3/3:5 disparity from asymmetric hDNA will depend solely on (1 ).…”