DNA
Abbreviation of deoxyribonucleic acid.
DNA ligase
width="400" valign="TOP"> A linking enzyme essential for DNA replication; catalyzes the
covalent bonding of the 3' end of a new DNA fragment to the 5' end of a growing chain.
DNA methylation
The addition of methyl groups (–CH 3 ) to bases of DNA after DNA synthesis; may serve as a
long-term control of gene expression.
DNA molecules
A nucleic acid that carries the genetic information in the cell and is capable of self-
replication and synthesis of RNA. DNA consists of two long chains of nucleotides twisted into
a double helix and joined by hydrogen bonds between the complementary bases adenine
and thymine or cytosine and guanine. The sequence of nucleotides determines individual
hereditary characteristics.
DNA polymerase
An enzyme that catalyzes the elongation of new DNA at a replication fork by the addition of
nucleotides to the existing chain.
DNA probe
A chemically synthesized, radioactively labeled segment of nucleic acid used to find a gene
of interest by hydrogen-bonding to a complementary sequence.
Domain
A taxonomic category above the kingdom level; the three domains are Archaea, Bacteria,
and Eukarya.
Dominance hierarchy
A linear "pecking order" of animals, where position dictates characteristic social behaviors.
Dominant allele
In a heterozygote, the allele that is fully expressed in the phenotype.
Dormancy
A period during which growth ceases and metabolic activity is greatly reduced; dormancy is
broken when certain requirements, for example, of temperature, moisture, or day length,
are met.