TABLE 4.

TRD in rad50, mre11, and xrs2 mutant cells

Genetic background and straina	Median distribution in strains
	% Precursor retainedb	Sample size (n)	No. of spore colonies	Pc
Background 1
Wild type	67	14	6
rad50	97	18	7	<0.01
mre11	97	6	4	<0.01
Background 2
Wild type	55	13	5
rad50	99.2	7	3	<0.01
xrs2	73	8	2	—d

^aAll strains listed under background 1 were isogenic to W303a. All strains listed under background 2 were derived from a cross between MBH9 and the nonisogenic strain TVL345 or a cross between MBR52-5b and the nonisogenic strain DVL227-6c. TVL345 is isogenic to the DVL227-6c background. Wild-type spore colonies from these crosses were used to determine the wild-type control value. 

^bThat is, the percent precursor retained after 20 generations (s2)/the percent precursor present in initial preculture (s0) calculated as described in Materials and Methods. 

^cP values obtained in comparisons between mutant and wild-type strains determined by the rank sum (Mann-Whitney) test. 

^d—, the hypothesis that xrs2 values are identical to wild-type or to rad50 values cannot be rejected at the 95% confidence level by the Mann-Whitney test.