Extended Data Table 1. Summary of data collected from sequenced passages.

Passage	Bases sequenced above Q20avg	Mutations detected above Q20avg	Average mutation frequency	Average mutations per genome	Variants detected*	% of alleles detected
2	1,405,927,958	378,993	2.70•10-4	2.01	15426	69.1
3	1,328,448,147	316,931	2.39•10-4	1.77	15780	70.7
4	1,490,238,776	397,442	2.67•10-4	1.98	17259	77.3
5	1,709,503,454	487,695	2.85•10-4	2.12	16778	75.2
6	1,647,601,130	498,477	3.03•10-4	2.25	17631	79.0
7	1,613,382,399	464,184	2.88•10-4	2.15	16670	74.7
8	1,438,501,772	470,689	3.27•10-4	2.43	16277	72.9

Data represented in this table are from consensus sequences filtered at average quality score 20. Variants(*) reported here are statistically significant (P value ≤ 0.05) by an exact binomial test using the average estimated error probability for each site, the coverage and number of mutations detected at each site (for each variant separately).