Final answer:
When a gene from the first locus does not produce a match in the Interactome database, genes with similar names should be tested. These paralogs could have similar functions and offer insights into the gene's biology.
Step-by-step explanation:
If investigating a gene from the first locus does not yield a match in the Interactome database, the next step would be to test genes with similar names, which are often referred to as paralogs. These are genes within the same species that have evolved by duplication but can carry out a similar function. It is common practice to search for similar genes when a direct match is not found, as they may provide clues about function or evolutionary history. Testing genes from a different species or with opposite functions would most likely not be helpful in this context, and genes from a different chromosome would usually not be considered paralogs. Therefore, genes with similar names provide the best alternative for testing after an initial non-match.