Hello,

I was wondering if there is a website in which I can retrieve the list of genes for each ontology. 

For example for the biological process "Regulation of Gene Expression," I would like to have all the list that belong to this ontology etc..

Thanks in advance
I recently wrote a small tool to fetch all the children of a given term in GO: http://lindenb.github.io/jvarkit/GoUtils.html

there is an example to fetch all the associated genes:

Use GO annotation to retrieve genes associated to GO:0005216 ‘ion channel activity’

    join -t $'\t' -1 1 -2 2 \
    	<(java -jar dist/goutils.jar -A 'GO:0005216' | cut -f 1 | sort | uniq) \
    	<(wget -q -O - "http://cvsweb.geneontology.org/cgi-bin/cvsweb.cgi/go/gene-associations/gene_association.goa_human.gz?rev=HEAD" | gunzip -c | grep -v '^!' | cut -f3,5 | uniq | LC_ALL=C sort -t $'\t' -k2,2) |\
    sort -t $'\t' -k2,2 |\
    grep SCN5A -A 10 -B 10
    
    (...)
    GO:0086006	SCN2B
    GO:0005244	SCN3A
    GO:0005248	SCN3A
    GO:0005248	SCN3A
    GO:0005248	SCN3B
    GO:0086006	SCN3B
    GO:0005248	SCN4A
    GO:0005248	SCN4A
    GO:0005248	SCN4B
    GO:0086006	SCN4B
    GO:0005244	SCN5A
    GO:0005248	SCN5A
    GO:0005248	SCN5A
    GO:0005248	SCN5A
    GO:0005248	SCN5A
    GO:0005248	SCN5A
    GO:0005248	SCN5A
    GO:0086006	SCN5A
    GO:0086060	SCN5A
    GO:0086061	SCN5A
    GO:0086062	SCN5A
    GO:0086063	SCN5A
    GO:0005248	SCN7A
    GO:0005248	SCN7A
    GO:0005248	SCN7A
    GO:0005248	SCN7A
    GO:0005248	SCN8A
    GO:0005248	SCN8A
    GO:0005248	SCN9A
    GO:0005248	SCN9A
    GO:0005248	SCN9A
    GO:0005272	SCNN1A
    (...)

