 Philosophers’ discussions of the concept of information in biology have also focused on its ontological reading. Three different philosophical accounts of information serve as exemplars of Downes’ three categories. Ulrich Stegmann (2005) provides an example of Downes’ first category with his analysis of template-directed synthesis. (Stegmann does explicitly allow that components other than nucleotide sequences might contain what he calls instructional information. However, his only example is a thought experiment involving enzymes linearly ordered along a membrane; nothing of the sort is known to actually exist or even seems very likely to exist.) Stegmann calls this the sequentialization view. Stegmann’s instructional account of genetic information requires that the component carrying the information satisfy the following conditions: an advance specification of the kind and order of steps that yield a determinate outcome if the steps are carried out. On his account, DNA qualifies as an instructional information carrier for replication, transcription and translation. The sequence of bases provides the order. The hydrogen bonding between specific bases and the genetic code provide the specific kinds of steps. And the mechanisms of replication, transcription, and translation yield certain outcomes: a copy of the DNA double helix, an mRNA, and a linear order of amino acids. Also, because DNA carries information for a specific outcome, an error can occur as the mechanism operates to produce that outcome; hence Stegmann’s account allows for errors and error-correcting mechanisms (such as proof reading mechanisms that correct DNA mutations). For more on this topic, see the entry on  biological information.