Sequence alignment is the procedure of comparing two (pairwise alignment) or more multiple sequences by searching for a series of individual characters or patterns that are in the same order in the sequences.
Global Sequence Alignment vs Local Sequence Alignment

Difference between Global and Local Sequence Alignment
Global Sequence Alignment
Local Sequence Alignment
In global alignment, an attempt is made to align the entire sequence (end to end alignment)            
Finds local regions with the highest level of similarity between the two sequences.
A global alignment contains all letters from both the query and target sequences
A local alignment aligns a substring of the query sequence to a substring of the target sequence.
If two sequences have approximately the same length and are quite similar, they are suitable for global alignment.
Any two sequences can be locally aligned as local alignment finds stretches of sequences with high level of matches without considering the alignment of rest of the sequence regions.
Suitable for aligning two closely related sequences.
Suitable for aligning more divergent sequences or distantly related sequences.
Global alignments are usually done for comparing homologous genes like comparing two genes with same function (in human vs. mouse) or comparing two proteins with similar function.

Used for finding out conserved patterns in DNA sequences or conserved domains or motifs in two proteins.

A general global alignment technique is the Needleman–Wunsch algorithm.
A general local alignment method is Smith–Waterman algorithm.
Examples of Global alignment tools:
  •  EMBOSS Needle
  • Needleman-Wunsch Global Align Nucleotide Sequences (Specialized BLAST)
Examples of Local alignment tools:
  •       BLAST
  •       EMBOSS Water
  •       LALIGN
This is summarized video on the topic


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