Table 2.
Effect of SPO13∷HO on meiotic recombination involving leu2∷cs
| Strain | Leu+∶Leu− | Total number of tetrads | Tetrads with no crossover between HIS4 and ADE1 | Tetrads with crossover between HIS4 and ADE1* | % crossover | Tetrads with coconversion of ADE1 |
|---|---|---|---|---|---|---|
| DAM 457 | 2∶2 | 286 | 264 | 21 | 7 | 1 |
| SPO11 | 3∶1 | 10 (3%) | 4 | 4 | 50 | 2 |
| 4∶0 | 0 | — | — | — | ||
| 0∶4 | 1 | — | — | 1 | ||
| 1∶3 | 5 (2%) | 0 | 4 | 1 | ||
| Total | 302 | |||||
| DAM 454 | 2∶2 | 457 | 421 | 36 | 8 | 0 |
| SPO11 | 3∶1 | 70 (12%)† | 28 | 38‡ | 52§ | 4 |
| SPO13∷HO | 4∶0 | 74 (12%)† | 28 | 18 | 23¶ | 28 |
| 0∶4 | 0 | |||||
| 1∶3 | 4 (1%) | 0 | 4 | |||
| Total | 605 |
Parental ditype (PD), tetratype (TT), and nonparental ditype (NPD) asci were identified with respect to the flanking ADE1 and HIS4 markers (see Fig. 1D). Tetrads in which ADE1 was coconverted were not considered. In (2∶2), (3∶1), and (1∶3) cases, all crossover tetrads are TT. Among the 18 4∶0 tetrads from DAM454, 15 were TT and 3 were NPD.
Statistically significant difference (P < 0.001) from the absence of SPO13∷HO.
In 34 of 38 cases a Leu+ spore experiencing gene conversion contained a crossover product, whereas in 4 cases the crossover did not involve the LEU2-containing chromatid.
The frequency of crossing over associated with conversion to Leu+ was determined after omitting four tetrads in which the adjacent ADE1 marker was coconverted and four tetrads in which crossing over did not involve the gene-converted chromatid.
For the 4∶0 tetrads, the frequency of crossing over was calculated on the basis of two gene conversion events per tetrad. Thus there were 15 TTs, with one crossover out of a possible two and three NPDs with two crossovers, of a total of 92 possible exchange events in 46 tetrads.