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From: winalski@psw.enet.dec.com (Paul S. Winalski)
Newsgroups: sci.bio
Subject: Re: Reconstructing cells from DNA
Message-ID: <1991Apr13.203239.22379@hollie.rdg.dec.com>
Date: 13 Apr 91 20:32:39 GMT
References: <18637@csli.Stanford.EDU>
Sender: news@hollie.rdg.dec.com (Mr News)
Reply-To: winalski@psw.enet.dec.com (Paul S. Winalski)
Organization: Digital Equipment Corporation
Lines: 38

In article <18637@csli.Stanford.EDU>,
cphoenix@csli.Stanford.EDU (Chris Phoenix) writes:
|>I recently heard of an experiment in which a paramecium (I think) had part of
|>its cell membrane removed, rotated, and put back, so that some of the spines
|>were backwards.  Its "descendants" also had backwards spines.  This implies
|>the possibility of one DNA set (sorry, I forget the fancy word) being 
|>consistent with several different cells.

Remember that paramecia are single-celled and reproduce mainly asexually
(although they do conjugate as well) by simple cell division.  The most likely
explanation is that the line of cell division crossed the rotated portion
of membrane, so that each of the descendents got part of the area with
backwards cilia (paramecia don't have spines).

|>   This would mean that:
|>1) Dinosaurs could not be replicated from their DNA alone, since there might
|>be differences between dinosaur cells and host cells that the dinosaur DNA 
|>could not fix.

This is quite likely, since it is the machinery of the egg's cytoplasm that
drives the early stages of development.  Incompatibilities between the
proteins coded for by the dinosaur DNA and the cytoplasmic machinery of the
host egg cell might well render the combintation non-viable.

|>2) Evolution of cells might take place by other mechanisms than just
|>mutation of DNA.  Non-genetic changes in cells might be hereditary.
|>In the case of sexual reproduction, I would expect that such changes
|>would be passed on only through the mother.
|>Is this totally off base, or is non-genetic evolution a possibility?
|>(Yes, I know mitochondria have their own DNA, and they evolve (or at 
|>least mutate.  I'm more interested, though, in changes to the cell
|>that do not involve any change in nucleic acid.)

I don't think that there are any cases of non-nucleic-acid-based hereditary
mechanisms in any known organisms.  Such mechanisms might be possible, but
living organisms don't make use of them.

--PSW