use strict;
use warnings;

while (<DATA>){
   chomp;
   next unless  my $i = (split/\t/,$_)[2];

   my $f =  $_;
      $i =~ s/ //g;

  (my $j = $i)  =~ s/G(.+)/Galpha-$1/;

   my @values = ($j =~ /(Galpha-[it])/ 
                    ? map{$1.$_}1..3 
                    : ($j)
                );

   for my $val (@values) {
      my $k =  $f;
      $k    =~ s/$i/$val/g;
      print "$k\n";
   }
}
__DATA__
biologist	xargon	Gi	question
perl	monks	G11	answer?
# prints
biologist       xargon  Galpha-i1       question
biologist       xargon  Galpha-i2       question
biologist       xargon  Galpha-i3       question
perl    monks   Galpha-11       answer?