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Glossary - X




X/A ratio X:A signal (S)  

A measure of the relative number of sex chromosomes (X) to autosomes (A) within the nucleus, which is critical in sex determination within that cell. Cells possessing a low ratio of X/A markers in their nucleus will adopt a male fate, while those with higher ratios (above a certain critical limit) will adopt female fates (Doniach and Hodgkin, 1984; Zarkower, 2006).

See Sex determination

X chromosome  

The number of copies of this chromosome determines the sex of the animal in C. elegans such that animals with two X chromosomes (XX) become hermaphrodites while animals with a single X chromosome (XO) become males (for details see Herman, 2006; Emmons, 2005; Ellis and Schedl, 2007; Zarkower, 2006). As hermaphrodites have two copies and males only have one, hermaphrodites reduce the expression from this chromosome in a process called dosage compensation (for details see Meyer, 2005).

See Sex determination

x neuron URX


Xenic medium

Xenic medium

A culture medium that includes one or more live microorganisms as part of the food for the cultured species (of nematode). Nematodes may be successfully raised upon bacteria, fungi, amoebae, dinoflagellates, or algae, although each nematode species may have a restricted set of foods which it tolerates (Nicholas, 1975). A culture medium containing only one strain of bacterium is termed monoxenic, or dixenic if it contains a mixture of two bacteria, or a bacterium plus an alga.

See Axenic medium
See Defined medium

X-gal 5-bromo-4-chloro-

A chemical substrate commonly used to detect lacZ enzyme activity which produces a blue stain visible by light microscopy.

See lacZ

XXX cell  

Two embryonic hypodermal cells (XXXL, XXXR) that may provide a scaffold for the early organization of ventral bodywall muscles and the various socket cells in the lateral and ventral lips. In the developing embryo, their cell bodies soon crawl posteriorly, and their processes separate the amphid nerve from the mechanosensory nerves in the late embryo. The XXX processes later retract, and the XXX cell bodies remain in the ventrolateral bodywall near the cell bodies of the posterior arcade and some socket cells where they perform a neurohumoral function, as they retain short processes bordering the pseudocoelom and contain some secretory vesicles. In early larval stages, XXX cells regulate dauer entry by secretion of several steroid signals (Gerisch et al., 2001; Jia et al., 2002) and in adults they may also have a role in cholesterol trafficking (Sym et al., 2000).

Edited for the web by Laura A. Herndon. Last revision: October 10, 2013. This section should be cited as: Herndon, L.A. and Hall, D.H. 2010. Glossary X. In WormAtlas.  doi:10.3908/wormatlas.6.24