Wiktionary
n. Sometimes used interchangeably with the word gene, a cistron is the unit of hereditary material (e.g. DNA) that encodes one protein.
WordNet
Wikipedia
A cistron is a gene. The term cistron is used to emphasize that genes exhibit a specific behavior in a cis-trans test; distinct positions (or loci) within a genome are cistronic.
For example, suppose a mutation at a chromosome position x is responsible for a recessive trait in a diploid organism (where chromosomes come in pairs). We say that the mutation is recessive because the organism will exhibit the wild type phenotype (ordinary trait) unless both chromosomes of a pair have the mutation ( homozygous mutation). Similarly, suppose a mutation at another position, y, is responsible for the same recessive trait. The positions x and y are said to be within the same cistron when an organism that has the mutation at x on one chromosome and has the mutation at position y on the paired chromosome exhibits the recessive trait even though the organism is not homozygous for either mutation. When instead the wild type trait is expressed, the positions are said to belong to distinct cistrons / genes.
For example, an operon is a stretch of DNA that is transcribed to create a contiguous segment of RNA, but contains more than one cistron / gene. The operon is said to be polycistronic, whereas ordinary genes are said to be monocistronic.
The words cistron and gene were coined before the advancing state of biology made it clear that the concepts they refer to are practically equivalent. This principle explains many instances of synonymity in the life sciences.
Usage examples of "cistron".
The word cistron has been used for a unit defined in this way, and some people use the word gene interchangeably with cistron.
The only way to tell where one cistron ends and the next begins would be to read the symbols on the tape, looking for end of message and start of message symbols.
A single cistron is likely to be much less than 1 per cent of the length of a chromosome.
The answer is that one gene in the sense of a cistron probably cannot.
The Selfish Cistron nor The Selfish Chromosome, but The slightly selfish big bit of chromosome and the even more selfish little bit of chromosome.
Even a cistron is occasionally divisible and any two genes on the same chromosome are not wholly independent.
To define a gene as a single cistron is good for some purposes, but for the purposes of evolutionary theory it needs to be enlarged.
Even a diamond is not literally everlasting, and even a cistron can be cut in two by crossing-over.
The largest practical unit of natural selection-the gene-will usually be found to lie somewhere on the scale between cistron and chromosome.
Even a group of several neighbouring cistrons can expect to live many generations before being broken up by crossing over.
Perhaps two cistrons which have a beneficial effect only when they are both present-they complement or reinforce each other in some way-will be brought close to each other by means of inversion.
A dozen cistrons may be so close to each other on a chromosome that for our purposes they constitute a single long-lived genetic unit.
As the cistrons leave one body and enter the next, as they board sperm or egg for the journey into the next generation, they are likely to find that the little vessel contains their close neighbours of the previous voyage, old shipmates with whom they sailed on the long odyssey from the bodies of distant ancestors.
Neighbouring cistrons on the same chromosome form a tightly-knit troupe of travelling companions who seldom fail to get on board the same vessel when meiosis time comes around.
Every sentence ever written down is sent into the world to be winnowed or thrive according to the same accountability principle as those cistrons and their experimental apparatus.