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quadrivalent See tetrad (second definition).
quantitative genetics The area of genetics concerned with the inheritance of continuously-varying traits. Most practical improvement programs involve the application of quantitative genetics.
quantitative inheritance Inheritance of measurable traits (height, weight, colour intensity, etc.) that depend on the cumulative action of many genes.
quantitative trait A measurable trait that shows continuous variation; a trait that can not be classified into a few discrete classes.
quantitative trait locus (QTL) A locus that affects a quantitative trait. The plural form (quantitative trait loci) is also abbreviated as QTL.
quantum (L. quantum, how much) An elemental unit of energy. Its energy value is hv, where h, Planck's constant, is 6.62 × 10-27 erg-second and v is the frequency of the vibrations or waves with which the energy is associated. cf photon.
quantum speciation The rapid formation of new species, primarily by genetic drift (q.v.).
quarantine (It. quarantina, from quaranta, forty) Originally, keeping a person or living organism in isolation for a period (originally 40 days) after arrival to allow disease symptoms to appear, if there was any disease present. Now used for regulations restricting the sale or shipment of living organisms, usually to prevent disease or pest invasion of an area.
quiescent Quiet, at rest, but not necessarily dormant, and having the potential for resumed activity; can apply to non-meristematic cells.
QTL See quantitative trait locus.
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