noun A theoretical unit of heredity of living organisms which may take several values and (in principle) predetermines a precise trait of an organism's form (phenotype), such as hair color.
genes that confer resistance to certain infections
noun A segment of DNA or RNA from a cell's or an organism's genome, that may take several forms and thus parameterizes a phenomenon, such as (often) the structure of a protein.
A change in a gene is reflected in the protein or RNA molecule that it codes for.