Prohibited degree of kinship

In law, a prohibited degree of kinship refers to a degree of consanguinity (blood relatedness), or sometimes affinity (relation by marriage or sexual relationship) between persons that makes sex or marriage between them illegal.

An incest taboo between parent and child or two full-blooded siblings is a cultural universal. Taboos against sexual relations between individuals of other close degrees of relationship vary.

full and half siblings

uncles and niece; aunt and nephew

first cousins (which is counted as fourth degree of kinship in Roman civil law tradition)

Affinity (law)

Cousin marriage

Inbreeding

Mahram

– Catholic Encyclopaedia

"Consanguinity"

– Article regarding Texas nepotism statutes, published by the Texas Association of Counties.