Now, I encounter a confusion about gene info mapping between ensembl ID(database accession in Ensembl) and ENTREZ ID(gene accession in NCBI GENE). I've found that not all genes with ensembl ID possess corresponding ENTREZ IDs, but still annotate to specific GO terms. Could anybody help me make it clear? I want to know why, why did the researchers tolerate this kind of gene annotation?
Any answer or hint will be appreciated. Thx in advance.