mutation, spontaneous change to genetic material occurring during cell division in organisms such as grapevines. Since so many vine varieties are of ancient origin, they have accumulated a substantial load of mutations. ancient vine varieties were invariably dark-skinned; light-skinned varieties are the result of mutation. Generally mutations are deleterious, but man has had many centuries in which deliberately to select those vines which perform best (a process now formalized as clonal selection), so beneficial mutations have been maintained.
