Restriction enzyme analysis of amplicons derived from S7 of different passages of a mixture of reassortant and parental virus. Amplicons were digested with BglII and PstI. Segment S7 of BTV8 (S78) digested with PstI (unique for S78) results in fragments of 471 and 685 bps (see lane 8), whereas segment S7 of BTV6 (S76) digested with BglII (unique for S76) results in fragments of 536 and 620 base pairs (bps) (see lane 9). Several blind passages (p) of the initial mixture of reassortant BTV6/net08/S78 and parental virus BTV6/net08 were analyzed by digestion with both restriction enzymes; p1 (lane 1), p2 (lane 2), p4 (lane 3), p5 (lane 4), and p6 (lane 5). Passage 6 was cloned by end point dilution and two finally cloned reassortants BTV6/net08/S78 were passed twice and analyzed (lanes 6 and 7). Analysis of amplicons derived from segment S7 of BTV8/net06 and parental virus BTV6/net08 are presented in lanes 8 and 9, respectively.