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Word / termDefinition

X:A ratio

The ratio between the X chromosome and the number of sets of autosomes.

x axis

The horizontal axis in a Cartesian Coordinate System.

X chromosome

One of the two sex chromosomes, X and Y. In almost all sexually reproducing organisms, the X-chromosome defines female characteristics.

X chromosome inactivation

In female mammalian embryos, the early random inactivation of the genes on one of the X chromosomes, leading to mosaicism for functions coded by heterozygous X-linked genes

Xenobiotics

Molecules entering an organism that has no physiological function and is not found in an organism if not taken up by eating, breathing, or injury. The term xenobiotics is used to describe a foreign particle or molecule that is potentially dangerous or toxic.

Xenograft

Tissue or organs from an individual of one species transplanted into or grafted onto an organism of another species, genus, or family. A common example is the use of pig heart valves in humans.

Xenosome

A foreign body. Used to refer both to bits of debris which may be incorporated into the shells of some testate amoebae, and also to symbiotic algae lying inside other cells.

Xenotransplant (also known as xenoplastic transplantation, xenogeneic transplantation)

The act of putting in a xenograft.

Xeriscaping

a method of landscaping that uses plants that are well adapted to the local area and are drought-resistant. Xeriscaping is becoming more popular as a way of saving water at home.
More on xeriscaping: Colorado WaterWise Council

X-inactivation centre (XIC)

Locus on the X chromosome in mammals at which inactivation is initiated.

XIP

X-ray in plaster. Refers to an x-ray study performed while the examined part is in a cast.

x intercept

The value of x at the point where a curve crosses the x-axis.

XOP

X-ray out of plaster. Refers to an x-ray study performed after the examined part has been removed from a cast.

Xylophagous

Feeding on wood.

XML

eXtensible Markup Language. A markup language like HTML that lets individuals define and use their own tags.  XML has no built-in mechanism to convey the meaning of the user's new tags to other users.

X-ray

1. High-energy radiation with waves shorter than those of visible light. X-rays possess the properties of penetrating most substances (to varying extents), of acting on a photographic film or plate (permitting radiography), and of causing a fluorescent screen to give off light (permitting fluoroscopy). In low doses X-rays are used for making images that help to diagnose disease, and in high doses to treat cancer . Formerly called a Roentgen ray. 2. An image obtained by means of X-rays.

X-ray crystallography

A technique, using X rays, to determine the atomic structure of molecules that have been crystallized. A technique for deducing molecular structure by aiming a beam of X rays at a crystal of the test compound and measuring the scatter of rays.

X-ray diffraction

Technique involving shooting x-rays through a target substance to study its atomic structure.Used to study atomic structure of crystalline substances by noting the patterns produced by x-rays shot through the crystal.
When X-rays are fired at a crystalline sample placed in the X-ray camera, a proportion is diffracted by the regular crystal structure. These diffracted X-rays produce a pattern of lighter and darker lines on a film. The pattern on the film depends on what is in the sample and by reference to standard data this pattern can be used as a kind of 'fingerprint' to identify a wide variety of materials. Such materials include corrosion products on metals, pigments used on wall paintings, and inlaid decoration in jewellery. (Source:British Museum)