Gene copies vs. gene paralogs - what's the difference?
The general term "copies" has multiple meaning with reference to genes. In diploid organisms for example, we have two copies of each gene (except those on the Y chromosome). However, these copies are called alleles. Copies that are due to duplication are called parlalogs. There is no distance criterion for differentiating copies or parlalogs. Once duplicated, there are two copies. But the consequences of paralogy would depend on differences, so the question is interesting. At the first generation after duplication, if both copies included all of the upstream regulatory elements, it would be hard to identify which of the copies was the original, since they would both be identical. But over time, if one were to evolve a new function or (more likely) accumulate frameshift substitutions, the altered one would be called the paralogous copy (relative to comparisons across species).