my @array =
    map { /^(\d+)\.\.(\d+)$/ ? $1..$2 : $_ }
    split /,/,
    $seq;
[download]

If you're worried about overlaps and/or duplicates,

my %seen;
my @array =
    grep !$seen{$_}++,
    sort { $a <=> $b }
    map { /^(\d+)\.\.(\d+)$/ ? $1..$2 : $_ }
    split /,/,
    $seq;
[download]