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G

geminate species pair

Two little-differentiated species evolved from a close common ancestor.

gene frequency

The number of occurrences of an allele in a gene pool.

gene pool

The complete set of unique alleles in a species or population.

generation

A single step or stage in the succession of natural descent.

genetic drift

Change in the gene pool that occurs when the frequency of an allele changes over generations due to random chance.

genotype

The genetic makeup of an organism or group of organisms with reference to a single trait, set of traits, or an entire complex of traits. (adj. genotypic)

glochidium

The specialized larval form of freshwater pearl mussels that usually has hooks that enable it to attach itself to a host (e.g., to the gills of a fish) for a period of time before it detaches and falls to the bottom and takes on the typical form of a juvenile mussel. (pl. glochidia)

gradualism

The process of gradual evolutionary change over time.

gross anatomy

Anatomy of organs and their arrangements, usually studied without the use of high magnification.