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On-Line Glossary: G

Each entry consists of a term (in bold), a definition of the term, and a number in parentheses (0) indicating the source of the definition. Clicking on the speaker icon will give you the pronunciation of the term. (Be sure to close the window for the sound player after each use.) The pencil icon will give you a drawing, and the camera icon will give you a photograph.


gall. An abnormal plant structure formed in response to parasitic attack by certain microorganisms (bacteria, fungi, viruses) or insects. Galls may develop either by localized cell proliferation or increase in cell size. (16)

gametangium. A structure that contains gametes. (16)

gamete. A haploid cell or nucleus involved in sexual reproduction, during which two gametes fuse to form a zygote. (16)

gametogenesis. The development of gametes. (17)

gasteromycete. A member of the Gasteromycetes.

Gasteromycetes. The group of Basidiomycetes with spores borne in cavities within the fruit body. (17)

gel. A matrix of polyacrylamide, agarose or similar material in which the electrophoresis of molecules is carried out. (10)

gel electrophoresis. A type of electrophoresis in which the molecules in a sample moves through a gel composed of agarose or polyacrylamide. (16)

geminivirus. (From Latin gemini, "twins", for the typical double particles). Member of the only group of plant viruses with double particles, each particle containing circular or linear single-stranded DNA; this group is divided into two subgroups I and II (transmitted in a circulative manner by leafhoppers) and subgroup III (transmitted in a circulative manner by whiteflies or, in the case of some viruses in this group, mechanically transmitted). (5)

gene expression. The transcription of mRNA from the DNA sequence of a gene and the subsequent translation of that mRNA to give the protein gene product. Less strictly it can mean the transcription step alone. (10)

genetic code. The nucleotide sequence of a DNA molecule (or, in certain viruses, of an RNA molecule) in which information for the synthesis of proteins is contained. (16)

genital papillae. In nematodes: Tactile or sensory organs located on the male tail. (14)

genital primordium. In nematodes: The initial cells of the reproductive system. (14)

genome. The genetic information for an organism, consisting (in the case of viruses) of one or more species of either RNA or DNA, but not both. (5)

genotype. The genetic constitution of an organism. (16)

genus. A taxonomic rank above species and below family; the generic name of an organism is the first of the binomial. (Pl. genera.) (20)

germ tube. A short, hypa-like structure that develops from certain types of spores upon germination. (16)

germination. In bacteria or fungi, the process by which a spore gives rise to a vegetative cell or hypha. (16)

germination by repetition. On the germination of a spore, the formation of a secondary spore rather than a germ tube. (16)

gill. A hymenium-covered, plate-like appendage that hangs from the under surface of the basidiocarp of some Hymenomycetes. (15)

glaucous. Having a bluish gray waxy surface. (21)

globose. Spherical, or nearly so. (17)

Gram reaction. The result of the Gram stain. (16)

Gram stain. An important bacteriological staining procedure discovered empirically in 1884 by the Danish scientist Christian Gram. When bacteria are stained with certain basic dyes, the cells of some species (Gram-negative species) can be easily decolorized with organic solvents such as ethanol or acetone. Cells of Gram-positive species resist decolorization. (16)

gubernaculum. In nematodes: Spicule guide; sclerotized accessory piece. (14)

guiding ring. In nematodes: Sleeve-like structure that surrounds and guides the stylet in genera of the Dorylaimoidea. Position varies among the genera from near apex to posterior portion of stylet. (14)

gummosis. A plant disease in which the lesions exude a sticky liquid. (16)

guttation. Exudation of water from plants, particularly along the leaf margin. (2)

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