Diverticulum
A pouch or sac that occurs normally or is created by herniation.

Divided gene
A split gene with exons at distinct loci, which must be transcribed separately and joined by trans splicing

DNA affinity chromatography
A technique used for the purification of sequence specific DNA binding proteins by their binding to a matrix to which the appropriate DNA fragments are attached .

DNA amplification
Multiplication of a segment of DNA into millions of copies chiefly by the polymerase chain reaction (PCR). Other amplification systems that are being developed include ligase chain reaction (LCR) and nucleic acid sequence dependent amplification.

DNA bank
Storage of DNA, which may or may not be the complete genome, but accompanied b inventory information.

DNA construct
A DNA molecules inserted into a cloning vector, usually a plasmid.

Divergent transcription
Initiation of transcription at two promoters that face opposite direction such that transcription proceeds in both directions from a central region.

DNA damage checkpoints
Checkpoints in the cell that arrest the cell cycle in response to DNA damage until the damage is repaired. For example, ionizing radiation activates several signal transduction pathways depending on the phase of the cell cycle. While cell cycle arrest in G1 and S prevents replication of damaged bases, arrest in G2 permits double strand breaks to be repaired before mitosis. Proteins encoded by the tumour suppressor genes ataxia telangiectasia mutated (ATM) and chk2, which encode protein kinases play a role in DNA damage check points Mutations in these genes cause cancer.

DNA delivery system
A term used for any method that transfers DNA or a gene f interest into a recipient host

DNA diagnosis
The use of DNA polymorphisms to detect the presence of a specific allele or DNA sequence that is associated with a disease or syndrome.

DNA directed RNA polymerase
See DNA polymerases.

DNA directed RNA polymerase
A group of enzymes that catalyses transcription to form RNA from a DNA template. They can initiate RNA synthesis de novo. In eukaryotes, three forms of the enzymes have been recognised based on the sensitivity to a amanitin, and the type of RNA synthesized

DNA driven hybridisation
The reaction of an excess of DNA with RNA. DNA fibre fish Fluorescence in situ hybridisation (FISH) applied to naked DNA.

DNA fingerprint
The unique pattern of DNA fragments that can be identified by Southern blotting (using a probe that binds to a polymorphic region of DNA) or by polymerase chain reaction(using primers flanking the polymorphic region). See genetic fingerprinting.

DNA fingerprinting
A technique developed by Alec Jeffreys for the identification of  individuals based on the fact that highly variable regions of the genome termed variable number of tandem repeats (VNTRs) in minisatellites are specific to each individual. VNTRs are inherited in a Mendelian fashion and are hypervariable when many alternate alleles exist in the population. VNTRs may be single locus repeats found at one locus or multi locus repeats found at many loci.

DNA fingerprinting may be carried out by digesting DNA with a restriction enzymes such as Hinfl which cuts outside VNTR region followed by side fractionation of DNA fragments by gel electrophoresis, Southern transfer and detection by hybridisation with a probe. PCR based method is however more sensitive and can amplify DNA with very low copy number.
The minisatellite probes 33.6 and 33.15 used by Jeffreys detect minisatellites at multiple loci and 17 variables fragments are generated for each individuals varying in size form 3.5 to 20 kb. Microsatellite tetranucleotide (CAGA) repeats are however preferred for forensic analysis. DNA fingerprinting works on the principle of exclusion and a single difference between sample and suspect rules out suspect. If the frequency of genotype is 10^-8, the probability of getting a chance match is 1 in 10⁸. DNA fingerprinting has applications in forensic science, paternity determination, pedigree analysis, migration studies and genetic analysis of agricultural crops and animals.

DNA footprinting
A technique for determining protein binding sites on DNA.
dna genes The genes encoding the DNA proteins (dnaA, dnaB, dnaC) that have a role in initiation of DNA replication at the replication origin in prokaryotes.

DNA glycosylase
An enzyme that recognises and removes bases that have undergone deamination generating apurinic or apyrimidinic sites.

DNA gyrase
An enzyme that catalyses the introduction of negative supercoils or relaxes positive supercoils in DNA. See Topoisomerase.