Burrows-Wheeler Aligner (BWA) is a program that aligns relatively short nucleotide sequences against a long reference sequence such as the human genome. It implements two algorithms, bwa-short and BWA-SW. The former works for query sequences shorter than 200Â bp and the latter for longer sequences up to around 100Â kbp. Both algorithms do gapped alignment. They are usually more accurate and faster on queries with low error rates.