College;
of;
Animal;
Science;
and;
Veterinary;
Medicine,;
Shandong;
Agricultural;
University,;
Taian;
271018,;
China;
College;
of;
Animal;
Science;
and;
Veterinary;
Medicine,;
Shandong;
Agricultural;
University,;
Taian;
271018,;
China;
subgroup; J; avian; leucosis; virus,; gp85; gene,; evolution,; immune; selection.;