GAMETES: Haploid sex cells that are made during meiosis. Females make gametes called ovum or eggs. Males make gametes called sperm.
GENE: A segment (piece) of DNA that codes for a protein. For example, cells must have the insulin gene in order to make the insulin protein.
GENE POOL: All of the alleles in a population's genes.
GENE THERAPY: Insertion of normal genes into human cells to correct genetic disorders.
GENETIC ENGINEERING: Method of cutting DNA from one organism and inserting the DNA fragment into a host organism of the same or different species.
GENETIC VARIATION: Different organisms in a population have slightly different genes (DNA). This produces differences in the organisms' physical appearance, or traits.
GENETICS: The study of heredity. Gregor Mendel is considered the father of genetics because of his early work with pea plants.
GENOTYPE: Pairs of alleles or genes for a particular trait. We usually write them as letters, like Bb. You cannot see an organism's genotype.
GENUS: A taxonomic ranking group composed of similar species. It is the first word of the two-part scientific name given to organisms.
GEOLOGIC TIME SCALE: A time scale that covers billions of years. The divisions are not based on fixed lengths of time, but on when major changes occured on Earth. It is divided into eons, eras, periods, and epochs.
GERM THEORY OF DISEASE: Infectious diseases are caused by microorganisms. "Germ" may refer to any bacteria, virus, fungus, protist, or prion. Microorganisms that cause disease are called pathogens.
GLUCOSE: A sugar made during the process of photosynthesis. The chemical formula for glucose is C6H12O6. Glucose is food for plants.
GOLGI BODY (APPARATUS): This organelle is the post office of the cell. It packages materials and then ships them out of the cell.
GROUNDWATER: Water that is beneath the surface of the earth. Groundwater is stored in aquifers.
GROUP: A vertical column on the periodic table. Elements in the same group often share similar chemical properties because they have the same number of valence electrons.