Etymology

A bit of etymology

ortho-

Prefix meaning straight; true; correct; perpendicular

log

A diary or frequently updated record of events (as in blog)

ortholog

A scientific term describing a particular kind of illustrative analogy or correspondence between two diverse things that are related by common descent.

In other words, this website is a log or collection of right-not-wrong stuff related through a common source or theme (namely, Interesting To Me). Though I've currently enabled comments, it's not really a discussion form (so dialogue wasn't appropriate).

There's a pleasing contrast with one of the definitions of analogue too, which in reference to electrical signals means varying continuously; whatever the quality of the content round here, I guarantee that it will vary discontinuously!

In case all that sounds pretentious, the truth: it's a scientific word and it nearly contains blog but not quite.[26]

Orthology of ortholog

orthology

The study of spelling

Problem: I'm English, therefore I write jewellery and traveller with two l's. Contrary to some expectations, true English word-nerdery requires that I spell hybridize; with a z rather than an s, as per the OED. All this means that I should be using the -logue ending but (a) orthologue.com was already taken, (b) I like the log-blog-ortholog symmetry, and (c) I don't mind being inconsistent[35]. Hence this is www.ortholog.com.

Scientific terms of analogy

These terms are usually used in genomics or in taxonomy, referring to things like the relationship between two genes or the common features of the Aves (birds). These terms are jargon par excellence because they have hardly any common currency. Worse still, they have a forbidding cachet: philosophers sometimes like them.

orthologs

Two things that share a common ancestor and some sort of functional similarity. Your leg and the leg of a kangaroo are orthologs, their common ancestor being the limb of some proto-mammal over a hundred million years ago.

paralogs

Two parts of something that share a common ancestor but do different jobs. Your leg and your arm are paralogous, sharing the same ancestor limb within your vertebrate lineage but having divergent functions. Your left leg and your right leg aren't paralogs, by the way.

homologs

A collective term for things similar in structure and evolutionary origin, though not necessarily in function. Orthologs and paralogs are types of homolog (there should be others; see the Koonin paper cited below).

seqlogs

A recently-coined and unpronounceable term for the relationship between two nucleic or amino acid sequences with measured similarity (this is one way in which ortholog is often erroneously used). This is supposed to be a term that doesn't imply or limit you to things with common evolutionary descent (at least until that is shown, in which case ortholog can be used). In our leg metaphor, your leg and something else exactly as long might be seen as a sort of seqlog.

For more information of homology and orthology, try the following:

• Information on orthology, paralogy etc. at NCBI
• A serious peer-reviewed review from Current Opinion in Genetics and Development (on the authors's website).
• The same author (Koonin) discusses the meanings and the spellings in his apology paper (available via Open Access).
• Bioinformatician Christopher Lewis at the University of Saskatchewan has some definitions of homolog, ortholog, and paralog.
• A diagram illustrating the difference between paralogs and orthologs on the Chlamydomonas section of the Los Alamos National Laboratory biosciences site.

Analogs and beyond

Apart from its other meanings, analogy can be loosely defined as describe a relationship between two things where some traits of one can be extrapolated onto the other. Your leg is like a table leg. It's the basis of metaphor i.e. is central to some of the cognitive processes that differentiate humans from other animals. Strictly speaking though, analog should only be used when the apparent or instructive similarity between the two things is not due to common ancestry (in other words, two things that are similar are either homologs of some sort or analogs of some sort because the terms are mutually exclusive). Your leg and the leg of a chair or an insect are analogous in this strict sense whereas your leg and kangaroo's are not-they're homologous, in particular they are orthologous rather than paralogous. Got all that?

If you really really care about other -logs, you might want to trawl the dictionaries for Antilogs, Catalogs, Cologs, Dialogs, Grammalogs, Mammalogs, Monologs, Pathologs, Prelogs, Prologs, Protologs, and Travelogs. Off you go. Or you could go and get some fresh air; don't forget to logue off first.