TABLE 5

Crossing over in disomic Ura+ gene convertants

ClassGenotype of disomeMatersa (%)Nonmatersb (%)
AHet. iTHR1 Het. iNAT (parental configuration)c14 (24)NA
BHet. iTHR1 Het. iNAT (nonparental configuration)d20 (34)NA
CHet. iTHR1 Het. iNAT (configuration unknown)eNA38 (59)
DHom. iTHR1 Het. iNATf14 (24)10 (15)
EHet. iTHR1 Hom. iNATf9 (16)15 (23)
FHom. iTHR1 Hom. iNATg1 (2)2 (3)
% CO frequency74h>38i (72j)
  • Disomic Ura+ gene convertants selected from spores of BR4633 were analyzed for crossing over in the iTHR1-iNAT interval. Het., heterozygous; Hom., homozygous; NA, not applicable.

  • a A total of 58 mating-competent disomes were scored by tetrad analysis.

  • b A total of 65 nonmating disomes were analyzed by PCR.

  • c The two chromatids retained the parental configuration of markers. One carried iTHR1, but not iNAT; the other carried iNAT, but not iTHR1.

  • d Both chromatids displayed a recombinant configuration of markers. One carried both iTHR1 and iNAT; the other chromatid carried neither marker.

  • e Classes A and B cannot be distinguished by PCR analysis.

  • f These classes result from crossing over in the iTHR1–iNAT interval.

  • g This class represents MII disomes carrying sister chromatids.

  • h CO frequency was calculated as the sum of classes B, D, and E divided by the sum of all classes and multiplied by 100.

  • i CO frequency represents the minimum frequency; it is the sum of classes D and E divided by the sum of all classes and multiplied by 100.

  • j CO frequency was calculated on the basis of the assumption that class C contains disomes with the nonparental configuration of markers (i.e., like class C) and that the frequency of these disomes relative to those with the parental configuration (i.e., like class B) is the same as it is among mating-competent disomes. Thus, the CO frequency was calculated as the sum of classes D and E plus 0.59 × class C divided by the sum of all classes and multiplied by 100.