Consanguinity: Close blood relationship, sometimes used to denote human inbreeding. Mating of closely related persons can cause significant genetic disease in offspring. Everyone carries rare recessive genes that, in the company of other genes of the same type, are capable of causing autosomal recessive diseases. First cousins share a set of grandparents, so for any particular gene in one of them, the chance that the other inherited the same allele from the same source is one in eight. For this reason, marriage between first cousins (not to mention closer relatives) is generally discouraged, and in many areas of the world is illegal. Mating between more distant relatives carries lesser risks. In families where a recessive genetic disorder is known or suspected to be present, genetic testing and counseling are advised, even if the level of consanguinity is very low (as, for example, in marriages between third or fourth cousins).