
798 Statistics and Data Analysis for Microarrays Using R and Bioconductor
to be present. For instance , the nucleus is “part of” the cell. This means that
every time there is a nucleus, this will be part of the cell. However, not all
cells have nuclei.
In order to increase the ontology’s ability to better described biologica l pro-
cesses, in March 2008 the GO Consortium introduced three new relationship
types: “regulates,” “negatively regulates,” and “positively regulates”
into the Biological Process ontology. These substituted some of the relation-
ships formerly described by “part of.” Currently, GO uses three qualifiers that
further re fine annotations, ...