Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!shelby!msi.umn.edu!noc.MR.NET!ns!pallas!beckfdp From: beckfdp@pallas.network.com (D. Pat Beckfield) Newsgroups: bionet.molbio.evolution Subject: Re: Homology/similarity/identity: proper usage. Message-ID: <1991Jan31.155713.27154@ns.network.com> Date: 31 Jan 91 15:57:13 GMT References: <3824@gazette.bcm.tmc.edu> Sender: news@ns.network.com Organization: Network Systems Corporation Lines: 37 Nntp-Posting-Host: pallas In article <3824@gazette.bcm.tmc.edu> steffen@mbir.bcm.tmc.edu (David Steffen) writes: > > I am again struggling with the proper use of the words "homology", >"similarity", and "identity" in comparing sequences. Specifically, we >have cloned and sequenced (a bit of) the rat homologue of the _lck_ >gene. The sequence of the mouse and human _lck_ genes is known. How >do we know what we have is the rat homologue? Because when we compare our >sequence to the published sequence, most of the nucleotides can be made >to match up with minimal futzing. So how do I say that? > [discussion of rationale deleted] > >-- >David Steffen >Department of Cell Biology, Baylor College of Medicine, Houston TX 77030 >Telephone = (713) 798-6655, FAX = (713) 790-0545 >Internet = steffen@mbir.bcm.tmc.edu As you're discussing semantics, it seems appropriate that I (a writer and BS in zoology) respond. The first question is does the rat sequence you're working with execute the same function as the similar sequences for mice and humans? If you don't know, is there a way to test it? Until you know this, what you have is a homomorphic string -- similar structure, but not necessarily having the same function. If they do carry out the same functions, but you're still concerned by evolutionary relations, you can call them "analogous" -- having the same function, but not necessarily the same origin. I hope this helps. -- D. Patrick Beckfield pat.beckfield@network.com 7600 Boone Ave N (612) 424-4888 Network Systems Corporation