degrees of freedom
The total number of items in a data set that are free to vary independently of each other. In testing for Hardy–Weinberg proportions this is the number of possible genotypes minus the number of alleles because the frequency of homozygous genotypes are determined by the frequency of heterozygous genotypes.

deme
A local conspecific group of individuals that mate at random.

demographic
Topics relating to the structure and dynamics of populations, such as birth, death, and migration rates.

demographic stochasticity
Differences in the dynamics of a population that are the effects of random events on individuals in the population.

dendrogram
A tree diagram that serves as a visual representation of the relationships between populations within a species.

derived
A derived character is one found only in a particular lineage within a larger group. For example, feathers are derived characters that distinguish birds from their reptile ancestors.

deterministic
Events that have no random or probabilistic aspects but rather occur in a completely predictable fashion.

diagnostic locus
A locus that is fixed, or nearly fixed for different alleles allowing differentiation between parental species, populations, or their hybrids.

dioecious
Varieties or species of plants that have separate male and female reproductive organs on unisexual individuals.

diploid
The condition in which a cell or individual has two copies of every chromosome.

directional selection
The selective increase in the frequency of an advantageous allele, gene, or phenotypic trait in a population.

disassortative mating
Preferential mating of individuals with different phenotypes.

discrete generations
Generations that can be defined by whole integers and in which all individuals will breed only with individuals in their generation (e.g., pink salmon or annual flowers without a seed bank).

dispersal
In ecological literature dispersal is the movement of individuals from one genetic population (or birth place) into another. Dispersal is also known as migration in genetics literature.

distinct population segment (DPS)
A level of classification under the ESA that allows for legal protection of populations that are distinct, relatively reproductively isolated, and represent a significant evolutionary lineage to the species.

DNA
Deoxyribonucleic acid.

DNA barcoding
The use of a short gene sequence from a standardized region of the genome that can be used to help discover, characterize, and distinguish species, and to assign unidentified individuals to species.

DNA fingerprinting
Individual identification through the use of multilocus genotyping.

Dobzhansky–Muller incompatibilities
Genic interactions between alleles at multiple loc in which alleles that enhance fitness within their parental genetic backgrounds may reduce fitness in the novel genetic background produced by hybridization.

dominance genetic variation
The proportion of total genetic variation that can be attributed to the interactions of alleles at a locus in heterozygotes.

dominant
An allele (A) whose phenotypic effect is expressed in both homozygotes (AA) and heterozygotes (Aa).

DPS
See distinct population segment.