Conservative replacement
A conservative replacement (also called a conservative mutation or a conservative substitution or a homologous replacement) is an amino acid replacement in a protein that changes a given amino acid to a different amino acid with similar biochemical properties (e.g. charge, hydrophobicity and size).
Conversely, a radical replacement, or radical substitution, is an amino acid replacement that exchanges an initial amino acid by a final amino acid with different physicochemical properties.