A first-degree relative (FDR) is a person's parent (father or mother), full sibling (brother or sister) or offspring.[1] It constitutes a category of family members that largely overlaps with the term nuclear family, but without spouses.[2]

If the persons are related by blood, the first degree relatives share approximately 50% of their genes. First-degree relatives are a common measure used to diagnose risks for common diseases by analyzing family history.[3]

See also


  1. ^ Talley, Nicholas (2007). Gastroenterology and Hepatology: A Clinical Handbook. p. 200.
  2. ^ Reiss, David (1981). The Family's Construction of Reality. Harvard University Press. p. 276. ISBN 9780674294158.
  3. ^ Ginsburg, Geoffrey (2008). Genomic and Personalized Medicine, Volumes 1-2. p. 482.