sub dna_mismatches {
    my $dna_standard   = shift;
    my $dna_to_compare = shift;
    my @mismatches = ( 0 );
#
# assume same length strands
#
    my $last_std = length($dna_standard);
    for ( 0 .. $last_std - 1 ) {
	if ( substr( $dna_standard, $_, 1 ) ne 
	     substr ( $dna_to_compare, $_, 1 )) {
	    $mismatches[0]++;
	    push @mismatches, $_ + 1;
	}
    }
    return \@mismatches;
}