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- Z -

Z-DNA; zig-zag DNA  A form of DNA duplex in which the double helix is wound in a left-hand, instead of a right-hand, manner. DNA adopts the Z configuration when purines and pyrimidines alternate on a single strand, e.g.,

zone of elongation  The section of the young root or shoot just behind the apical meristem, in which the cells are enlarging and elongating rapidly.

zoo blot  Hybridization of cloned DNA from one species to DNA from other organisms to determine the extent to which the cloned DNA is evolutionarily conserved.

zoo FISH Fluorescent in situ hybridization of DNA from one species on metaphase chromosomes of another species. Typically, the hybridization is done separately for DNA libraries representing each chromosome. The result is a fascinating picture of the regions of chromosomal homology between species.

zoospore  A spore that possesses flagella and is therefore motile.

zygonema (adj: zygotene)  Stage in meiosis during which synapsis occurs; coming after the leptotene stage and before the pachytene stage in the meiotic prophase.

zygospore (Gr. zygon, a yoke + spore)  A thick-walled resistant spore developing from a zygote resulting from the fusion of isogametes.

zygote (Gr. zygon, a yoke)  A diploid cell formed by the fusion of two haploid gametes during fertilization in eukaryotic organisms with sexual reproduction. It is the first cell of the new individual.

zymogen  Inactive enzyme precursor that after secretion is chemically altered to the active form of the enzyme.

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