TABLE 6

Recombination in mum4-1 spo13 strains

A. Allelic recombination
Relevant genotypeTrp prototrophs (X106)
StrainMitoticaMeioticb
Y1079MUM4 spo13::URA36.8 ± 0.9 (1.0)130 ± 36 (1.0)
Y0180mum4-1 spo13::URA36.3 ± 0.7 (0.9)160 ± 27 (1.2)
B. Reciprocal recombination
Chromosome IIIChromosome IV
StrainRelevant genotypeMAT-LEU2 distance (cM)cHIS4-LEU2 distance (cM)dPercent equational segregatione
Y1079MUM4 spo13::URA3371689
Y1080mum4-1 spo13::URA3321690
  • a Mitotic recombination frequencies are median frequencies ± SD derived from three independent cultures. Numbers in parentheses are the mitotic frequency normalized to the wild-type strain, Y1079.

  • b The meiotic recombination frequency ± SD represent the mean frequency from three independent cultures plate after 48 hr in sporulation medium. Numbers in parentheses are the meiotic frequency normalized to the wild-type strain, Y1079.

  • c Single crossover recombinant dyads for the MAT-LEU2 interval had the following phenotypes: α mater Leu + : a mater Leu+ and nonmater Leu: nonmater Leu+. The dyads with the phenotype a mater Leu: a mater Leu+ were scored as four-strand double crossovers. Dyads in which MAT and LEU2 have retained the parental configuration of markers probably arose from a reductional division that had not undergone exchange in this interval. The alternative possibility is that these dyads arose from a two-strand double crossover followed by equational division. If this were true, then an equal number of dyads displaying four-strand double crossovers and equational division would be predicted. There were significantly fewer of these types (1 vs. 10). Therefore, many of these dyads are probably the products of reductional chromosome segregation.

  • d Single crossovers in the LEU2-HIS4 interval produced dyads with the following phenotypes: Leu His+: Leu+ His+ and Leu+ His: Leu+ His+. Dyads exhibiting a mater: nonmater or a mater: non mater were scored as nondisjunctants (Klapholz and Esposito 1980) and were not included in the calculation of map distances. Map distance was calculated by using a derivation of Perkins’ formula (Perkins 1949) as follows: map distance = [single crossovers + 6(4-strand double crossovers)/total] × 100. Scoring was as follows: 107 dyads were scored for Y1079 and 96 dyads were scored for Y1080.

  • e Equational segregation was determined by examining the Trp phenotype of the dyad spore colonies as follows: equational segregation = Trppap: Trppap; reductional segregation = Trp: Trp; aberrant segregation = Trppap: Trp. Seven percent of dyads from Y1079 and four percent of dyads from Y1080 exhibited aberrant segregation.