Plz tell me wat are difference between cistron and gene.why in text given it is difficult to literally define a gene in terms of DNA sequence

dear nihala
A cistron is a term used to describe the locus (position) on a chromosome responsible for generating a protein.
In eukaryotic genetics, the concept is very similar to that of a gene. In eukaryotes, genes which function together in a single metabolic pathway may be located on different locations on a chromosome, or on different chromosomes altogether. In contrast, in prokaryotes, these genes are often located near each other, and are subject to a common "polycistronic" regulatory mechanism.
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REGARDS 

A gene is the portion of DNA that gets tracribed to give all types of RNAs whereas a cistron is referred to that portion of DNA which is capable of getting translated to polypeptides