What is the Difference Between Similarity and Identity in Sequence Alignment?

Similarity and identity are two key terms in the context of sequence alignment, which is a procedure in bioinformatics that arranges sequences of DNA, RNA, or protein to identify regions of resemblance due to functional, structural, or evolutionary relationships between the sequences. The main difference between similarity and identity in sequence alignment is:

Similarity: Sequence similarity refers to the resemblance between two sequences when compared. It is a general description of a relationship and is strongly correlated with percent identity. Sequence similarity can be calculated using the optimal matching algorithm, which finds the minimal number of edit operations (inserts, deletes, and substitutions) required to transform one sequence into an exact copy of the other sequence. The percentage sequence similarity is calculated as (1 - edit distance / unaligned length of the shorter sequence).
Identity: Sequence identity is the number of characters that match exactly between two different sequences. It is a more discrete measure compared to similarity. For example, a sequence with 100% identity means that all characters in the sequence are the same as in the reference sequence.

In summary, sequence similarity is a more general measure that describes the resemblance between two sequences, while sequence identity is a measure of the exact matching characters between two sequences. Sequence similarity is typically expressed as a percentage value, similar to sequence identity.

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What is the Difference Between Similarity and Identity in Sequence Alignment?

Comparative Table: Similarity vs Identity in Sequence Alignment

Here is a table comparing similarity and identity in sequence alignment:

Feature	Similarity	Identity
Definition	Resemblance between two sequences when compared.	The degree of identity between two sequences, i.e., the presence of the same subsequence.
Role in Sequence Alignment	Helps assess the likeness between two proteins, indicating the extent to which the residues are aligned.	Refers to the state of possessing the same subsequence.
Quantification	Similarity between two sequences is not typically quantified as a percentage.	Percent identity between two sequences is often quantified.
Evolutionary Relationship	Implies a common evolutionary origin between two sequences if their similarity is high.	Homology refers to the state of sharing a common evolutionary origin.
Alignment Process	Sequence alignment process involves finding the optimal alignment between two sequences, including gaps, using algorithms like FastA and LALIGN.	Alignment process helps identify regions of resemblance in DNA, RNA, or protein sequences resulting from functional, structural, or evolutionary relationships between the sequences.

Similarity in sequence alignment is the resemblance between two sequences when compared, and it is dependent on the identity of sequences. Sequence alignment helps to identify regions of resemblance in DNA, RNA, or protein sequences resulting from functional, structural, or evolutionary relationships between the sequences. Identity, on the other hand, refers to the exact state of possessing the same subsequence between two sequences.

Guilherme Mazui

Guilherme Mazui is graduated in journalism from the Federal University of Minas Gerais (UFMG) and a master's degree in Communication from the University of São Paulo (USP). In addition, he has experience in advertising writing and has worked as a content editor in several companies.