Conservative replacement

[1] There are 20 naturally occurring amino acids, however some of these share similar characteristics.

Although there are many ways to classify amino acids, they are often sorted into six main classes on the basis of their structure and the general chemical characteristics of their side chains (R groups).

[6] A conservative replacement is therefore an exchange between two amino acids separated by a small physicochemical distance.

Conversely, a radical replacement is an exchange between two amino acids separated by a large physicochemical distance.

Non-conservative replacements between proteins are far more likely to be removed by natural selection due to their deleterious effects.

A multiple sequence alignment , produced by ClustalO , of five mammalian histone H1 proteins.
Sequences are the amino acids for residues 120-180 of the proteins. Residues that are conserved across all sequences are highlighted in grey. Below each site (i.e., position) of the protein sequence alignment is a key denoting conserved sites (*), sites with conservative replacements (:), sites with semi-conservative replacements (.), and sites with non-conservative replacements ( ). This key uses PAM250 as a similarity measure. [ 3 ]