Table schema:
CREATE TABLE table_21481509_4 (r1b1a2__r_m269_ VARCHAR, r1b1c__r_v88_ VARCHAR)

Question: What percentage is listed in column r1b1a2 (r-m269) for the 77.8% r1b1c (r-v88)?
SQL: SELECT r1b1a2__r_m269_ FROM table_21481509_4 WHERE r1b1c__r_v88_ = "77.8%"