Darwiniam Fitness

The relative probability that a hereditary characteristic will be reproduced; the degree of the reproductive efficiency of the characteristic. Also known as Genetic Fitness.

Deletion

Loss of a chromosomal segment.

Devonian Period

A period of time lasting from 408 million to 360 million years ago in the earth's history.

Dinosaurs

A reptile that lived millions of years ago. Also classed as two types: mainly predatory and herbivorous types. Herbivorous types usually have long necks.

Diploidy

The condition of having two sets of chromosomes in each cell.

Directional Selection

The natural selection for traits at one extreme of a range of traits in a population and against intermediate traits and traits at the other extreme.

Divergence

The appearance and establishment of more than one species from one original species. Also known as cladogenesis.

Divergent Evolution

Evolutionary pattern that refers to the origin of new populations from old ones; more specifically, two or more species that originate from a common ancestor.

Diversifying Evolution

Natural selection for both ends of extreme or unusual traits in a population and against common traits. Similar to Disruptive Selection.

Deoxyribonucleic Acid (DNA)

The substance within the chromosomes that carries hereditary instructions and directs the production of RNA. The genetic information is contained within the sequence of nucleotides that make up the chainlike DNA molecules. This information determines the sequence of amino acids in the proteins, including enzymes responsible for the organism's fundamental life processes.

Dominant

An inherited trait expressed by an organism in its physical appearance regardless of whether the gene controlling the trait is homozygous or heterozygous; the dominant allele of that gene.

Duplication

Addition of a chromosomal segment.