A relationship by blood is also referred to as being related by consanguinity. A relationship by marriage is sometimes referred to as being related by affinity.
A husband and wife are related in the first degree by marriage. For other relationships by marriage, the degree of relationship is the same as the degree of underlying relationship by blood Example: John and Steve are brothers and are therefore second-degree relatives by blood. Johnís wife, Linda, is related to Steve in the second degree by marriage.
See Tex. Govít Code Section 573.025