Schematic view showing degrees of relatedness in a family history pedigree

First-degree relatives (designated "1") include parents, full siblings, or children. These individuals share approximately 50% of their DNA with the proband (closed circle). Second-degree relatives (designated "2") include grandparents, grandchildren, aunts, uncles, nephews, nieces, or half-siblings. These individuals share approximately 25% of their DNA with the proband. Third-degree relatives (designated "3") include first-cousins, great-grandparents or great-grandchildren. These individuals share approximately 12.5% of their DNA with the proband. Refer to UpToDate for additional discussions of pedigree interpretation and genetic risk assessment.