Thus, approximate methods are used, including (1)a progressive global alignment of the sequences starting with an alignment of the most alike sequences and then building an alignment by adding more sequences; (2)iterative methods that make an initial alignment of groups of sequences and then revise the alignment to achieve a more reasonable result (3)alignments based on locally conserved patterns found in the same order in the sequences (4)use of statistical methods and probabilistic models of the sequencesThus, approximate methods are used, including: (1) a progressive global alignment of the sequences starting with an alignment of the most alike sequences and then building an alignment by adding more sequences； (2) iterative methods that make an initial alignment of groups of sequences and then revise the alignment to achieve a more reasonable result； (3) alignments based on locally conserved patterns found in the same order in the sequences； (4) use of statistical methods and probabilistic models of the sequences