D Aspartic acid.

Darwinian fitness (see fitness)

decoding (see translation)

degenerate code A genetic code in which the number of sense codons is larger than the total number of amino acids and, consequently, some amino acids are specified by more than one codon. All known genetic codes are degenerate.

degenerate site A nucleotide site in a codon that can be occupied by more than one nucleotide and still code for the same amino acid.

degree of divergence The extent to which two homologous sequences differ from each other.

deleterious mutation A mutation that lowers the fitness of its carriers.

deletion The removal of one or more bases from a DNA sequence.

denaturation The loss of a protein's tertiary structure. Sometimes used improperly as a synonym of DNA melting.

dendrogram (see phylogenetic tree)

deoxyribonucleic acid (DNA) A macromolecular polymer of linked nucleotides in which the sugar residue is deoxyribose. Usually, double-stranded. The carrier of genetic information in all eukaryotes and prokaryotes, and in many viruses.

deterministic process A process, the outcome of which can be predicted exactly from knowledge of initial conditions.

diagnostic position (see informative site)

dichotomy (see bifurcation)

digestion The cutting of a double-stranded DNA by a restriction endonuclease.

diploid A chromosomal complement that contains two copies of each autosome.

directional selection A selective regime that changes the frequency of an allele in a specific direction, either toward fixation or toward elimination.

disjunction The separation of homologous chromosomes during meiosis or the separation of complementary chromatids during mitosis.

distance (see genetic distance)

distance matrix A matrix of genetic distances between taxa in a group under study.

divergence The splitting of a taxonomic unit into two (see sequence divergence)

DNA (see deoxyribonucleic acid)

DNA-DNA hybridization The formation of heteroduplex DNA.

domain1 (see functional domain)

domain2 (see urkingdom)

dominance (1) The property of an allele to manifest its entire phenotypic effect in the heterozygote. (2) In relation to fitness ...

donor site The 5' end of an intron.

dose repetition The presence of multiple copies of a DNA sequence which can be shown to produce increased quantities of a gene product relative to a single-copy sequence.

dot matrix A method of sequence alignment in which two sequences are written as column and row headings of a matrix and dots are put in those matrix elements that have identical column and row headings.

downstream.In the direction 3' of a reference point on a nudeic acid. In the direction of transcription.

drift (see random genetic drift)

duplex A double-stranded DNA or RNA, or a double helix formed by the complementary pairing of a single-stranded DNA with an RNA molecule.

duplication The presence or the creation of two copies of a DNA segment in the genome.

duplicative transposition (see replicative transposition)