Saint Sixtus III ; feast day March 28) was the pope from 432 to 440. A chief Roman priest when he succeeded Pope St. Celestine I on July 31, 432, Sixtus had previously been suspected of favouring Pelagianism (heretical doctrine that minimized the role of divine grace in man’s salvation), but on

XYY-trisomy, relatively common human sex chromosome anomaly in which a male has two Y chromosomes rather than one. It occurs in 1 in 500–1,000 live male births, and individuals with the anomaly are often characterized by tallness and severe acne and sometimes by skeletal malformations and mental

XYZ Affair, diplomatic incident that, when made public in 1798, nearly involved the United States and France in war. Pres. John Adams dispatched three ministers to France in 1797 to negotiate a commercial agreement to protect U.S. shipping. In Paris the ministers were approached by three French