Deal all,
  I exported human-pig ortholog relationship information from ensembl biomart. For gene SIRPA, it showed empty information of pig gene/transcrip/protein id nor any ortholog alignment information. But for most other genes, there are such information. So I thought pig doesn't have SIRPA. However, I found pig's SIRPA information when searching the gene in NCBI-gene. Why? I wondered maybe it's because they shared the same gene name but the properties of pig's SIRPA has changed quite a lot from human's SIRPA. But the gene description showed that they are quite the same. Could anyone explain this phenomenon a bit? Does ensembl biomart provide ortholog information incomplete? Thank you.

Best,
Yingzi
Orthologues in Ensembl are assigned using a [protein tree pipeline](http://www.ensembl.org/info/genome/compara/homology_method.html) which clusters proteins sequences using HMMs, then builds multiple alignments and reconciles against the species trees. The relationships between genes in these trees are used to [assign homologues](http://www.ensembl.org/info/genome/compara/homology_types.html).

These are recomputed with each Ensembl release and the pipeline was recently changed from using Blast for the clustering to HMMs, which has altered a lot of trees. The [previous version of Ensembl](http://jul2018.archive.ensembl.org/Homo_sapiens/Gene/Compara_Ortholog?anc=12844285;db=core;g=ENSG00000198053;g1=ENSSSCG00000007181;r=20:1894167-1940592;t=ENST00000356025) had human/pig orthologues with [many-to-many relationships](http://jul2018.archive.ensembl.org/Homo_sapiens/Gene/Compara_Tree?anc=12844285;db=core;g=ENSG00000198053;g1=ENSSSCG00000007181;r=20:1894167-1940592;t=ENST00000356025), which has changed. I think this needs to be re-examined and the orthologues restored. I recommend using the archive version of Ensembl for now.