Random spores | Individual spores from Set II tetrads | ||||
---|---|---|---|---|---|

Met^{+} spores
that are
NAT-hph
noncrossovers | Met^{+} spores
that are NAT-HPH
crossovers
(P < 0.0001) | Nonselected
NAT-hph
noncrossover
spores | Nonselected
NAT-HPH
crossover spores
(P = 0.0005) | Total
NAT-hph and
NAT-HPH spores | |

A. Crossing over in the lys5-NAT interval among individual spores^{a} | |||||

Crossovers | 82 | 37 | 518 | 25 | 543 |

Noncrossovers | 397 | 429 | 2063 | 212 | 2275 |

χ^{2} P (interference) | 0.29 (none) | <0.0001 (positive) | 0.48 (none) | 0.0012 (positive) | |

Random spores | Individual spores from Set II tetrads | ||||

Met^{+} spores
that are
NAT-hph
noncrossovers | Met^{+} spores
that are NAT-HPH
crossovers
(P = 0.0015) | Nonselected
NAT-hph
noncrossover
spores | Nonselected
NAT-HPH
crossover spores
(P = 0.029) | Total
NAT-hph and
NAT-HPH spores | |

B. Crossing over in the HPH-cyh2 interval among individual spores^{a} | |||||

Crossovers | 57 | 27 | 266 | 13 | 279 |

Noncrossovers | 422 | 439 | 2346 | 222 | 2568 |

χ^{2} P (interference) | 0.18 (none) | 0.007 (positive) | 0.67 (none) | 0.042 (positive) |

↵

A comparison of^{a}*MET13*prototrophic random spores derived from a*met13-1*/*met13-5*diploid (first two columns) with equivalent segregants obtained by treating the 1451 tetrads in set II as individual spores (last two columns). Only*NAT*-containing spores were counted so that crossover and noncrossover events were counted only once, to permit statistical comparisons with the random Met^{+}spore data.The χ

^{2}*P*-values at the heads of columns 2 and 4 compare the crossovers in those columns to the noncrossovers in columns 1 and 3, respectively. The χ^{2}*P*-values in the last rows of parts A and B compare the data in those columns with the total number of*NAT-hph*and*NAT-HPH*segregants in set II, treated as single spores. Random spores were obtained from a yeast diploid strain obtained by a cross between haploid strains isogenic to those used for tetrad analysis (Table 1, set II). The diploid used to generate Met^{+}random spores was derived from the haploids*MAT*α*lys5 NAT met13-1 cyh2 KAN*and*MAT***a***ade5,7 leu1 HPH trp5 met13-5 crl3*. The randomness of the spores was verified by monitoring phenotypes at both the*ADE5,7*and the*LEU1*loci (480 Ade^{−}and 465 Ade^{+}; 434 Leu^{−}and 511 Leu^{+}). Among Met^{+}spores, there were 466 crossovers (371 Nat^{−}Hph^{−}and 95 Nat^{+}Hph^{+}) and 479 noncrossovers (370 Nat^{+}Hph^{−}and 109 Nat^{−}Hph^{+}) for the flanking markers. The inequalities in both the crossover and noncrossover classes suggest that 78% of Met^{+}spores are the result of conversion of*met13-1*. This bias is expected from the sign and magnitude of the slope of the conversion gradient at the*MET13*locus, where*met13-5*is at the low-conversion end (J. McCusker and J. E. Haber, unpublished data).