Discontinuous replication
Describes the synthesis of DNA via short Okazaki fragments that are subsequently joined into c continuous strand.

Discontinuous variation
Phenotypic variation that involves distinct classes such as red versus white, tall versus dwarf.

Disinfection
is rarely possible. See disinfestation.

Disinfection
Destruction of pathogenic microorganism or their toxins and vectors by direct exposure to physical or chemical agents.

Disc electrophoresis
Discontinuous electrophoresis. A type of polyacrylamide gel electrophoresis in which the sample is electrophoresis. A type of polyacrylamide phases a low percentage stacking and a higher percentages resolving gel. This produced higher resolution between closely  migrating bands. See gel electrophoresis.

Disomy
(adj: disomic). Possessing two copies of a given chromosome. This is the normal state, the abnormal conditions being monosomy, trisomy and nullisomy (with one chromosome of a pair, three or one respectively). Abnormal disomic conditions  are also seen such as when both chromosomes of the pair are inherited from the same parent.

Dispense To remove a portion of a nutrient medium into containers, such as test tubes, jars, Erlenmeyer flasks, Petri dishes, etc.

Dispersed repetitive DNA
Moderately repetitive DNA found scattered throughout the genome in may species. Two classes of dispersed repeats SINES and LINES are abundant in mammals. SINES are short interspersed nuclear elements. The Alu element in humans and B1 element in mice are SINES.
LINES are long interspersed nuclear elements. L1 element, the most abundant of these elements, is 6kb in length with a copy number of 10⁵. Both Alu and L1 elements make up 10 per cent of the human genome. They are found in introns and flanking region of genes. These sequencing constitute parasitic or selfish DNA without any known function. However, they may have an effect on evolution by influencing or disrupting gene sequences. They are also postulated to have a role in replication and gene regulation.

Dispersion The degree of scatter or variation about the central value.


Dispersive replication
A disproved model of replication in which new DNA synthesis is interstitial and each daughter cell receives a mixture of parental and newly synthesized strand.

Dissecting microscope
A microscope with a low magnifying power of about 50 X, that is used to examine or excise small plant or animal parts.

Dissection
Separation of a tissue by cutting for analysis or observation.

Dissociation constant
1. The equilibrium constant (kd) for the dissociation of a complex containing two or more biomolecules into its components . For eg. The dissociation of an enzyme from its substrate. 2.The dissociation constant (ka) of an acid that describes its dissociation into its conjugate base and proton.

Dissociator (Ds) elements
Defective derivatives of the autonomous activator  (Ac) elements. They may be derived from autonomous elements by loss of trans acting functions needed for transposition.

Distance matrix
A method used to present the results of the calculation of an optimal pairwise alignment score. The matrix field (l.j) is the score assigned to the optimal alignment between two residues (up to a total of l by j residues) from the input sequences. Each entry is calculated from the top left neighbouring entries using a recursive equation.

Distance measure
A function that associates a none negative numeric value with a pair of biosequences. The shorter the distance between he sequences the greater is the similarity. For example, the distance between glycine and alanine is small, whereas that between glycine and arginine is large.

Distillation
The process of heating a mixture to achieve separation of more volatile from the less volatile substances, followed by cooling and condensing the resulting vapour to produce a more nearly pure or refined substances.

Distributed annotation system
a client server system in which a single client integrates information from multiple servers. It allows a single machine to collect genome annotation information from multiple distant web sites, collate the information, and display it to the user in a single view.

Distributed database A database containing data and associated software distributed over a network or the internet. See CORBA, middleware.

Disulfiram
A drug that decreases catecholamine biosynthesis by inhibiting dopamine b hydroxylase. This is useful as an antihypertensive agent and for the treatment of alcoholism

Disulphide (disulfide) bond
A chemical bond that stabilizes the three dimensional structure of proteins. These bonds form between cysteine residues in the same or different peptide molecules. Also termed disulphide bond.

Disulphide (disulfide) bridge
See disulphide bond.

Ditype
In fungi, a tetrad containing two types of meiotic products (spores). For example, 2AB and 2ab. See tetrad.

Diuresis
Excretion of unusually large quantities of urine.

Diuretic
An agent that increases urine excretion.

Diurnal
A term that describes the occurrence of an event at least once every 24 hours. See circadian