Gene

A gene is a discrete hereditary factor responsible for an observable trait in an organism. The precise combination of genes found in an individual defines its genotype. The collection of observable traits displayed by an individual based on its genotype is referred to as its phenotype. A gene may code for more than one trait, and a trait may be determined by more than one gene.

Genes are composed of DNA and are maintained within the chromosomes of cells in pairs. In sexually reproducing organisms, each parent contributes one gene to a pair. The dominant gene in a pair determines the displayed trait while the recessive gene is merely carried.

Sexual reproduction provides a means of reshuffling combinations of genes. Mutation is an important mechanism by which novel variation is introduced. Genes are the basis upon which natural selection acts.

Genes responsible for alternate varieties of a given trait are known as alleles. Evolution then can be seen as a change in the frequency of alleles in a population over time.

The study of genes is known as genetics. Gregor Mendel, the "father of modern genetics," is credited with first making the observation that distinct, alternate traits will be inherited in mathematically predictable ways.