Table 4.

Frequency of viable interspecific hybrids

CrossaNo. of putative hybrids on SDbFrequency of putative viable hybridd
A
 Y185 × Y170∼104 32 × 10−2
 Y184 × Y2451,0003.8 × 10−2
 Y185 × Y2441,5004.5 × 10−2
 Y169 × Y2441,5004.5 × 10−2
 Y170 × Y2451,0003.3 × 10−2
B
 Y185 × Y3396c 6.7 × 10−6
 Y184 × Y34450c 10−4
 Y185 × Y34470c 4.7 × 10−5
C
 Y345 × Y257∼103 ∼3.3 × 10−3
 Y345 × Y344∼103 ∼6.7 × 10−4
 Y257 × Y3445 + 50e 7.8 × 10−5
  • a A, crosses within the sensu stricto group; B, crosses between yeasts belonging to the sensu stricto and sensu lato groups; C, crosses between yeasts belonging to the sensu lato group. Note that only interspecific crosses, which gave viable hybrids, are shown in this table.

  • b All of the parental strains were tested for revertants on SD, and the reversion rate was shown to be lower than 10−7 for each of them. Therefore, when a colony appeared on SD, it was likely to be a hybrid because only approximately 107 parental cells, including zygotes, were plated on the selective plate.

  • c Small colonies.

  • d Frequencies of putative viable hybrids are the ratio between the number of colonies on SD plates and the presumed number of hybrids plated out.

  • e Five large and 50 small colonies.