Table 9.

Synthetic lethality between null alleles of several microtubule cytoskeleton components^a

	Inferred double mutants	Observed double mutants	p
bim1Δ × num1Δ	8	0	0.005
bim1Δ × bub3Δ	18	0	0.00002
bim1Δ × bik1Δ	8	0	0.005
bim1Δ × tub2-201	6	6	n/a
bik1Δ × bub3Δ	16	0	0.00006

^aCrosses between various mutants in microtubule cytoskeleton components (bim1Δ, bik1Δ, num1Δ, bub3Δ, and tub2-201) were performed as described in MATERIALS AND METHODS, and the resulting tetrads (at least 20 for each combination) were sporulated and dissected. Data from all crosses which failed to yield viable double mutants are shown. Only information from nonparental ditype tetrads is shown, because in those tetrads identification of the double mutants by the auxotrophic markers which marked each deletion was unambiguous, even when the two disruptions were marked by the same auxotropy. The number of double mutants dissected from nonparental ditype tetrads is shown in “Inferred double mutants” whereas the number of these spores which formed colonies is shown in “Observed double mutants.” The p value is the result of a χ² test using the null hypothesis that in the nonparental ditype tetrads, the 50% viability observed is randomly distributed. In all cases, except with bim1Δ × tub2-201, included as an example of a cross from which viable double mutants were recovered, there is significant deviation from the distribution predicted by the null hypothesis, suggesting that the lethality is caused by the double-mutant genotype.