TABLE 4.

Spontaneous mutators in cultures of AS18-29 detected on selection plates with different cell densities^a

No. of AS18-29 cells	No. of cultures	No. of cul-tures with no mutators	Mutator plating efficiency (%)	No. of mutators found	No. of nonmu-tators	% Muta-tors
105	355	327	10	43	48	47
104	344	323	50–100	21	27	44

^aClose to 700 cultures were plated at two different cell densities, and the number of mutators found in samples of each culture was recorded. Each sample represented either 10⁴ or 10⁵ cells. The frequency of mutators in the population was determined from the fraction of cultures with no mutators and the plating efficiency at the respective cell density (see Materials and Methods).