Heredity<span>, </span><span>the sum of all biological processes by which particular characteristics are transmitted from parents to their offspring. The concept of heredity encompasses two seemingly paradoxical observations about organisms: the constancy of a </span>species<span> from generation to generation and the </span>variation<span> among individuals within a species. Constancy and variation are actually two sides of the same coin, as becomes clear in the study of </span>genetics<span>. Both aspects of heredity can be explained by </span>genes<span>, the functional units of heritable material that are found within all living </span>cell<span>s. Every member of a species has a set of genes specific to that species. It is this set of genes that provides the constancy of the species. Among individuals within a species, however, variations can occur in the form each </span>genetic<span>s, providing the genetic basis for the fact that no two individuals (except identical twins) have exactly the same traits.</span>
