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x The basic number of chromosomes in a polyploid series, monoploid = x; diploid = 2x; triploid = 3x; etc.
xanthophyll (Gr. xanthos, yellowish brown + phyllon, leaf) A yellow chloroplast pigment.
X-chromosome A chromosome associated with sex determination. In most animals, the female has two, and the male has one X chromosome. The opposite occurs in birds, in which the equivalent is the Z chromosome.
xenia The immediate effect of pollen on some characters of the endosperm.
xenobiotic A chemical compound that is not produced by living organisms; a manufactured chemical compound.
xenotransplantation The transplantation of tissue from one species to another species, typically from non-human mammals to humans. This technology has become very important because of a worldwide shortage of human organs for humans requiring a new organ. The most popular non-human species involved in this technology is the pig.
xerophyte (Gr. xeros, dry + phyton, a plant) A plant very resistant to drought or that lives in very dry places.
X-linkage See X-linked.
X-linked The presence of a gene on the X chromosome. a.k.a. X-linkage.
X-linked disease A genetic disease caused by an allele at a locus on the X-chromosome. In X-linked recessive conditions, a normal female "carrier" passes on the allele on her X chromosome to an affected son.
X-ray crystallography The deduction of crystal structure from analysis of the diffraction pattern of X-rays passing through a pure crystal of a substance.
xylem (Gr. xylon, wood) A complex tissue specialized for efficient conduction of water and mineral nutrients in solution. Xylem may also function as a supporting tissue, particularly secondary xylem.
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