Avunculate Unions

The coefficient of inbreeding (F) for progeny resulting from an uncle-niece marriage is approximately 0.125, indicating that, on average, 12.5% of their gene loci are homozygous due to shared ancestry. This is double the coefficient found in first-cousin marriages (F=0.0625).

• Ancient Egypt: Ankhesenpepi II and her nephew Merenre Nemtyemsaf I; Ahmose I and his half-niece Ahmose-Sitkamose; Thutmose I and his half-aunt Mutnofret; Pepi II Neferkare and his aunt Neith; Pinedjem I and his half-aunt Duathathor-Henuttawy; Menkheperre and his niece Istemkheb; Shabaka and his aunt Qalhata.
• Ancient Greece & Rome: Perictione and her uncle Pyrilampes; Leonidas I of Sparta and his half-niece Gorgo; Arybbas of Epirus and his niece Troas; Alexander I of Epirus and his niece Cleopatra of Macedon; Lucius Tarquinius Superbus and his brother Arruns Tarquinius respectively married sisters Tullia Major and Tullia Minor; Cyrus the Great and his aunt Amytis of Media; Herod the Great married an unnamed niece; Salome I and her uncle Joseph; Antipater II and his half-niece Mariamne III; Herod Antipas and his half-niece Herodias; Salome (daughter of Herod II and Herodias) married Philip the Tetrarch (her half-uncle and half-granduncle); Herod of Chalcis and his niece Berenice; Philip III of Macedon and his half-niece Eurydice II of Macedon.
• Hellenistic & Seleucid Dynasties: Mithridates III of Pontus and his grand-niece Laodice; Seleucus II Callinicus and his aunt Laodice II; Antigonus II Gonatas and his niece Phila; Demetrius II Aetolicus and his half-aunt Stratonice of Macedon; Antiochus X Eusebes and his possible half-aunt Cleopatra Selene of Syria.
• Ptolemaic Dynasty: Ptolemy VIII Physcon and his niece Cleopatra III of Egypt; Ptolemy X Alexander I and his niece Berenice III of Egypt; Ptolemy XII Auletes and his half-niece Cleopatra V.
• East Asian Dynasties: Emperor Hui of Han and his niece Empress Zhang Yan (192 BC); Sun Xiu and his niece Empress Zhu (Eastern Wu); Gwangjong of Goryeo and his half-niece Lady Gyeonghwa; Injong of Goryeo and his aunts Princess Yeondeok and Princess Bokchang; Emperor Kōan and his niece Oshihime; Yamato Takeru and his aunt Futaji Irihime; Emperor Kinmei and his half-niece Ishi-Hime; Emperor Jomei and his niece Empress Kōgyoku, and his aunt Princess Tame; Emperor Kōtoku and his niece Princess Hashihito; Emperor Tenmu and his nieces Empress Jitō, Princess Ōta, Princess Ōe, and Princess Niitabe; Prince Kusakabe and his aunt Empress Genmei; Emperor Shōmu and his aunt Empress Kōmyō; Emperor Junna and his niece Princess Seishi; Emperor Suzaku and his niece Princess Hiroko; Emperor En'yū and his niece Princess Sonshi; Emperor Go-Ichijō and his aunt Fujiwara no Ishi; Emperor Go-Suzaku and his aunt Fujiwara no Yoshiko, and his niece Fujiwara no Genshi; Emperor Horikawa and his half aunt Princess Tokushi; Emperor Nijō and his half aunt Princess Yoshiko; Emperor Go-Fukakusa and his aunt Fujiwara no Kimiko; Emperor Fushimi and his aunt Tōin Sueko; Anjong of Goryeo and his half-niece Queen Heonjeong.
• Medieval & Early Modern Europe: Emperor Claudius and his niece Agrippina the Younger (49 AD); Tiberius Claudius Atticus Herodes and his niece Vibullia Alcia Agrippina; Byzantine Emperor Heraclius and his niece Martina (c. 613); Rupert I, Elector Palatine and his great-grandniece Beatrix of Berg (1385); John, Constable of Portugal and his half-niece Isabel of Barcelos (1424); Afonso V of Portugal and his niece Joanna of Castile (1475); Jacques of Savoy, Count of Romont and his niece Marie of Luxembourg, Countess of Vendôme (1484); Joanna of Naples and her half-nephew Ferdinand II of Naples (1496); Ferdinand II of Aragon and his half-grandniece Germaine of Foix (1505); Philip II of Spain and his niece Anna of Austria (1570); Charles II, Archduke of Austria and his niece Maria Anna of Bavaria (1571); Ferdinand II, Archduke of Austria, and his niece Anne Juliana Gonzaga (1582); John III of Rietberg and his niece Sabina Catharina of East Frisia (1601); Maximilian I, Elector of Bavaria and his niece Archduchess Maria Anna of Austria (1635); Prince Maurice of Savoy and his niece Princess Luisa Cristina of Savoy (1642); Karl Eusebius, Prince of Liechtenstein and his niece Johanna Beatrix of Dietrichstein (1644); Philip IV of Spain and his niece Mariana of Austria (1646); Borso d'Este and his niece Ippolita d'Este (1647); Louis Charles d'Albert, 2nd Duke of Luynes and his aunt Princess Anne de Rohan-Montbazon (1661); Leopold I, Holy Roman Emperor and his niece Margaret Theresa of Austria (1666); Adolphus Frederick II, Duke of Mecklenburg-Strelitz and his half-grandniece Princess Johanna of Saxe-Gotha (1702); Prince Augustus Ferdinand of Prussia and his niece Margravine Elisabeth Louise of Brandenburg-Schwedt (1755); Peter III of Portugal and his niece Maria I of Portugal (1760); Prince Benedetto, Duke of Chablais and his half-niece Princess Maria Ana of Savoy (1775); Infanta Benedita of Portugal and her nephew José, Prince of Brazil (1777); Infante Antonio Pascual of Spain and his niece Infanta Maria Amalie of Spain (1795); Infante Francisco de Paula of Spain and his niece Princess Luisa Carlotta of the Two Sicilies (1819); Ernest I, Duke of Saxe-Coburg and Gotha and his niece Duchess Marie of Württemberg (1832); Prince Francis, Count of Trapani and his niece Archduchess Maria Isabella of Austria (1850); Duke Nicholas of Württemberg and his half-niece Duchess Wilhelmine of Württemberg (1868); Prince William of Hesse-Philippsthal-Barchfeld and his half-niece Princess Juliane of Bentheim and Steinfurt (1873), and later his half-niece Princess Adelaide of Bentheim and Steinfurt (1879); Amadeo I of Spain and his niece Maria Letizia Bonaparte (1888); Prince William of Hesse-Philippsthal-Barchfeld and his half-niece Princess Juliane of Bentheim and Steinfurt (1873), and later his half-niece Princess Adelaide of Bentheim and Steinfurt (1879).
• 19th & 20th Centuries: James Mayer de Rothschild and his niece Betty Salomon von Rothschild (c. 1825); Ferdinand VII of Spain and his niece Maria Isabel of Portugal (1816), and later his niece Maria Christina of the Two Sicilies (1829); Gustav, Landgrave of Hesse-Homburg and his niece Princess Louise of Anhalt-Dessau (1798–1858) (1818); Leopold, Grand Duke of Baden and his half-grandniece Princess Sophie of Sweden (1819); Ernest I, Duke of Saxe-Coburg and Gotha and his niece Duchess Marie of Württemberg (1832); Prince Francis, Count of Trapani and his niece Archduchess Maria Isabella of Austria (1850); Mongkut and his half-grandniece Somanass Waddhanawathy (1851), and his half-grandniece Debsirindra (1851), and later his half-grandniece Phannarai (1851); Svasti Sobhana and his half-niece Abha Barni, and later his half-niece Chavi Vilaya Gagananga; Richard von Metternich and his niece Pauline von Metternich (1856); Ignacy Łukasiewicz and his niece Honorata Stacherska (1857); Porfirio Díaz, 33rd President of Mexico, and his niece Delfina Ortega Díaz (1867); Duke Nicholas of Württemberg and his half-niece Duchess Wilhelmine of Württemberg (1868); Prince William of Hesse-Philippsthal-Barchfeld and his half-niece Princess Juliane of Bentheim and Steinfurt (1873), and later his half-niece Princess Adelaide of Bentheim and Steinfurt (1879); Amadeo I of Spain and his niece Maria Letizia Bonaparte (1888); Henryk Sienkiewicz, Polish novelist, and his niece Maria Babska (1904); Alois Hitler and his niece Klara Hitler, parents of Adolf Hitler (1885); Zachariah Fugate and his aunt Mary Smith (1890s); Arturo Grullón, Dominican Republic painter and doctor, and his niece Filomena Grullón (1909); Anton Mussert and his aunt Maria Witlam (1917); Enrique Loynaz, a Cuban patriot, married his niece Carmen Loynaz (1922); Prince Vongsanuvatra Dhevakul and his half-niece Princess Kamolpramot Kitiyakara (1930s); Norodom Sihanouk and his half-aunt Sisowath Pongsanmoni (1945), and later his half-aunt Sisowath Monikessan; Julio César Turbay Ayala, 25th President of Colombia, and his niece Nydia Quintero Turbay (1948).