Update: Improved the performance.

sub ntuples{
    my( $n, $s ) = @_;
    my $b = $n -1;
    my $n2 = length( $s ) - $n +1;
    return unpack "(A$n X$b)$n2", $s;
} ;;

$genome = 'AACCCDGYAEELPSWWYAOOLLLSSBBBDDD';;

print join ' - ', ntuples( $_, $genome ) for 2 .. 5;;

AA - AC - CC - CC - CD - DG - GY - YA - AE - EE - EL - LP - PS - SW - 
+WW - WY - YA - AO - OO - OL - LL - LL - LS - SS - SB - BB - BB - BD -
+ DD - DD
AAC - ACC - CCC - CCD - CDG - DGY - GYA - YAE - AEE - EEL - ELP - LPS 
+- PSW - SWW - WWY - WYA - YAO - AOO - OOL - OLL - LLL - LLS - LSS - S
+SB - SBB - BBB - BBD - BDD - DDD
AACC - ACCC - CCCD - CCDG - CDGY - DGYA - GYAE - YAEE - AEEL - EELP - 
+ELPS - LPSW - PSWW - SWWY - WWYA - WYAO - YAOO - AOOL - OOLL - OLLL -
+ LLLS - LLSS - LSSB - SSBB - SBBB - BBBD - BBDD - BDDD
AACCC - ACCCD - CCCDG - CCDGY - CDGYA - DGYAE - GYAEE - YAEEL - AEELP 
+- EELPS - ELPSW - LPSWW - PSWWY - SWWYA - WWYAO - WYAOO - YAOOL - AOO
+LL - OOLLL - OLLLS - LLLSS - LLSSB - LSSBB - SSBBB - SBBBD - BBBDD - 
+BBDDD
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