Dr. Paul's Virtually Biology Show.

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G

Gamete. A haploid cell for use in reproduction to produce a diploid zygote upon fusing with another such haploid cell.
Gametophyte. A haploid multicellular plant that products gametes by mitosis.
Gene. A region of DNA associated with the expression of one or another form of a characteristic usually due to the protein coded for by the region of DNA. Alternate forms of a gene are called alleles.

Gene flow. The movement of alleles from one population to another via migration and interbreeding of migrant individuals.

 

Genetic code. A table displaying the possible messenger RNA codons and their corresponding amino acids and the stop codons.

Genetic drift. The loss of genes(alleles) from a population do to chance effects, specifically "sampling error" in small populations. The idea is that in small populations not all the different alleles at a particular locus will be passed on equally just by chance.

Genome. The complete set of genes in a cell. In a eukaryotic cell this may be taken to include the nuclear genes and genes in the mitochondria and other DNA bearing organelles.
Genotype. The genetic make-up of an organism, often with respect to a particular gene pair under study.
Germ cell. One of a lineage of cells differentiated for the production of haploid cells for gametes or spores in plants by meiosis. In contrast somatic cells give rise to new cells by mitosis. In plants the situation gets confused.
Germ layer. In animals one of three tissue lineages that form during and are characteristic of an embryonic stage called gastrulation; Ectoderm, mesoderm, endoderm. These tissue layers are important because most of the organs in the body can be traced to one or another of these layers.
Gill. An evagination of an animal's body that serves as a respiratory surface.
Glomerulus.The first section of the kidney's nephron where filtration takes place. The glomerulus is made of a tight network of capillaries called the glomerular capillaries from which the blood filtrate is collected into the proximal collecting tubule of the nephron.
Glucagon. A hormone produced by the pancreas that stimulates the break down of glycogen and the release of glucose into the blood stream.
Glucose. A six carbon simple sugar(C6H12O6) commonly used as a source of energy by the organism. Glucose is produced by plants and either immediately used for cellular respiration or used to make polysaccharides such as starch or cellulose.
Glycerol. An alcohol with three hydroxyl groups. Glycerol is an oil alcohol that is an important component of fats and oils.
Glycogen. A polysaccharide produced by animals for short term energy storage. In humans and other mammals glycogen is stored in the liver and in the muscles. One of its uses is to help regulate blood glucose levels. Runners load up on "carbs" the day before a race to increase short term glycogen reserves in the skeletal muscles.
Glycolysis. The anaerobic breaking apart of glucose to yield ATP and 2 pyruvic acid molecules which happens in the cytoplasm of the cell.
Golgi body. A membranous organelle consisting of flattened sacs that serves as a way station and packaging site for materials synthesized by eukaryotic cells.

Gradualist model. The idea that species arise from pre-existing species by means of a set of slow evolutionary transitions from one form to another.

Granum. In chloroplasts a series of flattened sacs each of which is called a thylakoid. These are important as the site of the light dependent reactions of photosynthesis.

Ground tissue. In plants one of the three main tissue types. Ground tissue makes up the bulk of the tissue in plants, with the possible exception of woody plants. Ground tissues have a number of functions including: support, gas exchange, starch storage, water storage,and photosynthesis.
Guard cell. A specialized dermal cell in plants that is used to regulate the size of the pores(stoma) on the surface of plants through which gas exchange and water loss take place. Each stoma is surrounded by two lip like guard cells.