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From: cphoenix@csli.Stanford.EDU (Chris Phoenix)
Newsgroups: sci.bio
Subject: Re: Reconstructing cells from DNA
Message-ID: <18841@csli.Stanford.EDU>
Date: 24 Apr 91 17:29:05 GMT
References: <18637@csli.Stanford.EDU> <79788@bu.edu.bu.edu>
Organization: Center for the Study of Language and Information, Stanford U.
Lines: 36

In article <79788@bu.edu.bu.edu> colby@bu-bio.UUCP (Chris Colby) writes:
>In article <18637@csli.Stanford.EDU> cphoenix@csli.Stanford.EDU (Chris Phoenix) writes:
>>2) Evolution of cells might take place by other mechanisms than just
>>mutation of DNA. 
>	Evolution is defined as a change in the gene pool. So, changes
>in a heritable material must occur of evolution is to occur. So far
>DNA (and RNA) are the only two known genetic materials.

>>Non-genetic changes in cells might be hereditary.
>	This is like saying non-blue balls might be blue. If something
>is hereditary, it must be genetically based (although it would not
>neccesarily have to be genetic material in the form of nucleic acid).

OK, I used the wrong words.  I should have said "transmissible to 
offspring" instead of "hereditary" and "change in characteristics of
cell" rather than "evolution".  That said, my question remains:  Is
it possible to have a transmissible change take place in a cell that
does not involve nucleic acid?
Here's a possible example:  Prions do not contain nucleic acid, but can
make more prions inside a cell.  If a prion is introduced to a cell, and 
the cell then produces offspring, the offspring will presumably have 
the prion in them.  From then on, the descendants would all have the 
prion (plus whatever effects the prion had), whereas the ancestors didn't.
But the cell's nucleic acid would be unchanged.
BTW, can you give me an example of genetic material that is not in the
form of nucleic acid?

>>In the case of sexual reproduction, I would expect that such changes
>>would be passed on only through the mother.
>	Why?

Because the (egg) cells the mother contributes are much larger and more 
complex than the (sperm) cells the father contributes.  Eggs would be more
likely than sperm to preserve non-nucleic changes.

Chris Phoenix		cphoenix@csli.stanford.edu