Social organization in Akan kingdoms in Ghana is based on matrilineal descent.
Each town or village has a royal family - the family that first settled there.
From this royal family the chief and the queen mother are selected by the elders of the royal family.
Occasionally the chief and queen mother are related to each other as mother and son, but more often they are uncle and niece, aunt and nephew, cousins, etc.
A carved wooden stool is the symbol of authority, and the chief and queen mother are “enstooled,” as European monarchs are enthroned.
Queen mothers are the “most important” officials involved in selection of the chief and are–sometimes called the “supreme king makers”.
The queen mother is knowledgeable of the clan genealogy, and she may have her own court and be assisted by other clan officials.
“One of the queen mother’s major roles ... is to advise the chief on all matters”
Reference: http://rainqueensofafrica.com/2011/03/information-on-the-queen-mother-tradition-among-the-kwahu-people-of-ghana/