Consanguineous

 Consanguineous is the mating between two individuals who are related as second cousins or closer. Mating between relatives is important for recessive alleles to become homozygous. When a recessive is rare, it is more likely to become homozygous through inheritance from a common ancestor than from parents who are completely unrelated. Therefore, consanguineous marriages increase risk for congenital malformations and autosomal recessive diseases.

 References

1. Daniel L. Hartl & Maryellen Ruvolo (2012). Genetics: analysis of genes and genomes (8th edition)

2. Hamamy, H. (2012, July). Consanguineous marriages: Preconception consultation in primary health care settings. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3419292/