X chromosome: A sex chromosome present in two copies in the homozygous sex and in one copy on the heterozygous sex.
X chromosome-autosome balance system: A genotypic sex determination system. The main factor in sex determination is the ratio between the numbers of X chromosomes and autosomes. Sex is determined at the time of fertilization, and sex differences are assumed to be due to the action during development of two sets of genes located in the X chromosomes and in the autosomes.
X chromosome nondisjunction: An event occurring when the two X chromosomes fail to separate in meiosis so that eggs are produced either with two X chromosomes or with no X chromosomes, instead of the usual one X chromosome.
X-linked: Referring to genes located on the X chromosome.
X-linked dominant trait: A trait due to a dominant mutant gene carried on the X chomosome.
X-linked recessive trait: A trait due to a recessive mutant gene carried on the X chromosome.
X-ray diffraction analysis: A technique used in identifying minerals present in artifact raw materials; it can also be used in goemorphological contexts to identify particular clay minerals in sediments, and thus the specific source from which the sediment was derived.
X-ray fluourescence spectrometry (XRF): A method used in the analysis of artifact composition, in which the sample is irradiated with a beam of X-rays which excite electrons associated with atoms on the surface.
XTENT modeling: A method of generating settlement hierarchy, that overcomes the limitations of both central place theory and Thiessen polygons; it assigns territories to centers based on their scale, assuming that the size of each center is directly proportional to its area of influence. Hypothetical political maps may thus be constructed from survey data.
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