In addition to patrilineal and matrilineal principles, some unilineal systems combine both rules to form a dual descent structure as illustrated in the following diagram.
In this arrangement Ego is a member of two separate and fundamentally distinct groups: a uterine group through his mother (in red) and an agnatic group through his father (in blue). Where dual systems are employed, one set of groups will tend to take on complementary functions in relation to the other. For example, among the Yako of Nigeria, patrilineages are important for the allocation and inheritance of land, while matrilineal groups determine the ownership of movable property such as cattle.
Note that siblings are both agnatic and uterine relatives. Non unilineal kin are termed cross relatives because, at some point in the sequence of linking relatives, a gender change occurs. Individuals 19, 20, 27, and 28 are Ego's cross cousins because the parents involved are opposite sexed siblings, a brother and sister in each case. One set of Ego's grandchildren, 35 and 36, are also his cross relatives because of a male-female sequence from ego to his daughter.