$ perl -Mstrict -Mwarnings -E '
my @array =
   map {
       my( $key ) = keys %$_;
       map $key, 1 .. $_->{ $key };
       } { A => 3 }, { T => 4 }, { C => 2 }, { G => 5 };

say for @array;'
A
A
A
T
T
T
T
C
C
G
G
G
G
G
$