A patronymic surname, from given names.
"The genealogist noted that Allison is often a patronymic surname derived from the male given name Alison."
Allison is a surname derived from Middle English as a diminutive form of the names Alan, Alexander, or Alice combined with the suffix "-son." It originally functioned to denote "little" or "son of" one of these given names before becoming established in its current usage.