The X chromosome occupies an exceptional place in the mammalian genome. Together with the Y chromosome, the X chromosome differentiates the sexes. Males have one X chromosome and a Y chromosome and females have two X chromosomes. Because o...

An X terminal is a computer that lacks a disk. Accordingly, X terminals do not have (house) resident applications. X terminals are designed to connect a user to network applications that are running in an X server; a server operating in a ...

(b. 1946), East Timorese resistance leader. As the leader of the struggle for independence, Xanana Gusmão became the most important resistance figure of East Timor. Born on 20 June 1946 in Laleia, East Timor, José Alexandre &...

Zubiri, Xavier(1898–1983) Xavier Zubiri, the Spanish Christian ontologist, was born in San Sebastián. He was professor of the history of philosophy in Madrid from 1926 to 1936 and in Barcelona from 1940 to 1942, after an abse...

Designating a foreign and usually harmful substance or organism in a biological system. Xenobiotic, derived from the Greek root xeno, meaning "stranger" or "foreign," and bio, meaning "life," descr...

Xenogamy (also called outbreeding) is a term used to describe the union of genetically unrelated organisms within the same species. Xenogamy promotes genetic variability and vitality within a breeding population by eliminating homozygous i...

Xenon is the fifth element in Group 18 of the periodic table, a group of elements known as the noble gases or inert gases. Xenon has an atomic number of 54, an atomic mass of 131.29, and a chemical symbol of Xe. Xenon is a colorless, odor...

The Greek historian, essayist, and military expert Xenophon (ca. 430-ca. 355 BC) was the most popular of the Greek historians. He facilitated the change from the Thucydidean tradition of history to rhetoric. The son of Gryllus of the Athen...

The roots of Xerox Corporation and its history of innovation started growing back in 1938. In October of that year, patent attorney Chester Carlson (1906–1968) invented the first xerographic image. Carlson believed that the world ne...

When The X-Files premiered on the Fox network in the fall of 1993, no one predicted the degree of success that the show would eventually enjoy. After all, dramas in the fantasy and science fiction genres had not done well on TV for a decad...

(2002 est. pop. 2.7 million). Xi'an is the provincial capital of Shaanxi Province in central China. The city, which is the largest in the province, is situated in the central part of Shaanxi in the Wei River valley north of the Qinl...

The term "Xiang" refers to the people and the local sublanguage used in Hunan, a province in southeast-central China; Xiang is derived from the older literary name of Hunan. It is estimated that more than 25 million Chinese (...

By the end of the nineteenth century, nearly every political and intellectual leader in China saw the need for change. Some, such as Sun Yat-sen (1866–1925), felt that rather than reforming the imperial system, China needed a thorou...

X-linked agammaglobulinemia (XLA) or Bruton's agammaglobulinemia is present at birth (congenital) and is characterized by low or completely absent levels of immunoglobulins in the bloodstream. Immunoglobulins are protein molecules in blood...

X rays are a form of high-energy electromagnetic radiation. Electromagnetic radiation, or light energy, occurs as a continuous gradient, or spectrum, of forms. Exhibiting wave-like properties, the electromagnetic spectrum consists of light...

X-ray crystallography is an experimental technique for determining the arrangement of atoms in a crystalline material using highly energetic electromagnetic radiation. X-ray crystallography provides the most direct and accurate means of es...

Stars radiate energy in many wavelengths. Visible light, the wavelength we see with the naked eye, is only one small part of the electromagnetic spectrum. Toward the short-wavelength end, beyond visible blue light and invisible ultraviolet...

Xu Guangqi (1562-1633) was a Chinese scholar-official, who rose to one of the highest government positions in the Ming dynasty, pioneered in the introduction of Western science and technology into China, and became one of the "Three Pillar...

Hsüan Tsang (ca. 602-664) was the most famous Chinese Buddhist pilgrim and traveler in India and a translator of Buddhist texts. His "Hsi-yü Chi," or "Record of Western Countries," remains an indispensable source book to students...

XX male syndrome occurs when the affected individual appears as a normal male, but has a female genotype (two X chromosomes). Two types of XX male syndrome can occur: those with detectable SRY gene and those without detectable SRY. SRY is ...

The term "xylene" refers to any of three benzene derivative isomers that share the same chemical formula, C6H4(CH3)2, but differ in their molecular structure. They are useful as solvents, as additives to improve the octane ra...