A second-degree relative (SDR) is someone who shares 25% of a person's genes. It includes uncles, aunts, nephews, nieces, grandparents, grandchildren, half-siblings, and double cousins.[1][2][3]

See also


  1. ^ "Breast and Ovarian Cancer and Family History Risk Categories". Center for Disease Control.
  2. ^ "First, Second and Third Degree Relative". Blue Cross Blue Shield.
  3. ^ "NCI Dictionary of Genetics Terms". Cancer.gov.