A chromosome is a long, continuous strand of DNA that contained genes and regulatory elements. It is a macromolecular unit of genetic information. Humans have 23 chromosome pairs.
Chromosomes can be negatively impacted by:
- excess or deficiency of trace elements;
- industrial waste byproducts in air and water;
- vitamin deficiencies:
- viral contaminants;
- magnetic field failure;
- increase in visible light;
- potassium overexposure;
- calcium resorption;
- long-term disease exposure;
- extraterrestrial diseases;
- airborne particles (inert or carcinogenic);
- gravitational variations;
- solar field variations;
- neutrino bombardment;
- chemical exposure;
- nuclear radiation;
- gamma ray exposure;
- ultraviolet radiation; and
- parasitic organisms. (TNG: "When The Bough Breaks")
In 2369, Julian Bashir and Jadzia Dax ran a chromosome scan of a clone of Ibudan. (DS9: "A Man Alone")
In 2372, The Doctor used undamaged chromosomes from Denara Pel's cerebellum to recreate her original DNA code. (VOY: "Lifesigns")
When the Silver Blood USS Voyager and its crew began to deteriorate from subspace radiation in 2375, The Doctor found that their chromosomes were breaking down on a molecular level. (VOY: "Course: Oblivion")
The Brunali made microgenetic alterations in the 3rd, 13th, and 17th chromosomes of certain children so that they would produce a spaceborne virus, turning them into weapons against the Borg. (VOY: "Child's Play")
During an away mission in the Delta Flyer in 2376, Mortimer Harren asserted that genetics, not environment, were the determining factor in personality. In response, Captain Janeway jokingly asked, "How's your 13th chromosome? Missing a couple of base pairs in gene 178?" (VOY: "Good Shepherd")