01    my ( $pattern, $mismatches_allowed ) = @_;

##</code><code>##

02    if ( $mismatches_allowed == 0 ) { return $pattern }

##</code><code>##

03    elsif ( length($pattern) <= $mismatches_allowed ) {
04        $pattern =~ tr/ACTG/./;
05        return $pattern;
06    }

##</code><code>##

07    else {

##</code><code>##

08        my ( $first, $rest ) = $pattern =~ /^(.)(.*)/;

##</code><code>##

09        my $after_match = make_approximate( $rest, $mismatches_allowed );

##</code><code>##

10        if ( $first =~ /[ACGT]/ ) {
11            my $after_miss = make_approximate( $rest, $mismatches_allowed - 1 );
12            return (?:$first$after_match|.$after_miss);
13        }

##</code><code>##

14        else { return $first$after_match }
15    }