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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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