TABLE 2.

Effect of selection pressure on the number of wild-type genome copies

Parameter	Puromycin concn (μg ml−1)
	0	0.15	0.6	2.5
Selection pressure	−	+	++	+++
No. of wild-type genomes
After generation 1	2	1	1	1
After generation 8	10	5	1	2
After generation 14	21	17	9	3
Avg increase per generation	1.62	1.31	0.69	0.15