Disease resistance
The ability to remain healthy by resis1jing disease or the disease agent. Disease resistance or tolerant is a subject of intense interest in biotechnology.

Disease-free
A plant or animal certified through specific tests as being free of specified pathogens. Disease-free should be interpreted to mean "free from any known disease" as "new" diseases may yet be discovered to be present. cf disease indexing.

Disjunction
Separation of homologous Chromosomes during anaphase I of meiosis; separation of sister chromatids during anaphase of mitosis and anaphase II of meiosis. As soon as the sister chromatids have separate, they are each called a chromosome. See non-disjunction.

Dislocation
A linear crystalline defect around which there is an atomic misalignment.

Disomy
(adj: disomic) The presence of a pair of specific chromosome. This is the normal condition, and abnormal occurrences are monosomy (q.v), trisomy (q.v.) and nullisomy (with respectively one chromosome of a pair, three or none). There are also abnormal disomic conditions, such as when both chromosomes of the pair were inherited from the same parent.

Dissolve
Pass chemicals into solution.

Dissolved oxygen (DO)
The amount of molecular oxygen dissolved in water.

Di-sulphide bond
A chemical bond that stabilizes the three-dimensional structure of proteins, and hence the protein’s normal unction. They form between cysteins residues in the same or different peptide molecules. a.k.a. di-sulphide bridge.

Di-sulphide bridge
See di-sulphide bond.