What percentage is listed in column r1b1a2 (r-m269) for the 77.8% r1b1c (r-v88)?
create table table_21481509_4 (r1b1a2__r_m269_ varchar, r1b1c__r_v88_ varchar, PRIMARY KEY (r1b1a2__r_m269_))
select r1b1a2__r_m269_ from table_21481509_4 where r1b1c__r_v88_ = "77.8%"