<p>I am using biomart to convert multiple gene names to Entrez IDs, however, I found that for some gene names, it returned multiple IDs. Shouldn&#39;t the name and ID have a one to one correspondence? I also tried to use all the returned IDs and search in NCBI, but it seems only one of them is the same with my inquiry. For example, try &quot;POTED&quot; in biomart, it returns three IDs - &quot;388468,339010,317754&quot;. But only searching 317754 in NCBI will give you the right gene symbol POTED. Why biomart returns multiple IDs?</p>

<p>Gene names aren&#39;t unique. The closest to an actually unique ID that I normally use would be Ensembl gene IDs (this is why I normally recommend using Ensembl annotations, when available).</p>

<p><strong>Edit</strong>: I&#39;ll add that a single Entrez ID can have multiple gene names (on more than one chromosome or even on different strands of the same chromosome). Yeah, that can make life difficult.</p>
