Re: Article: Parasite genes reveal long sexual history
From: Perplexed in Peoria (jimmenegay_at_sbcglobal.net)
Date: 01/31/05
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Date: Sun, 30 Jan 2005 22:17:20 -0500 (EST)
"William L Hunt" <wlhunt@earthlink.net> wrote in message news:ctjg4k$qcp$1@darwin.ediacara.org...
> On Sat, 29 Jan 2005 13:59:43 -0500 (EST), "Perplexed in Peoria"
> <jimmenegay@sbcglobal.net> wrote:
>
> >
> >"Robert Karl Stonjek" <rstonjek@bigpond.net.au> wrote in message news:ctfbc4$2eg5$1@darwin.ediacara.org...
> >> Giardia Bares All: Parasite genes reveal long sexual history
> >> Christen Brownlee
> >>
> ...
> [snip]
> ...
> >PS: My joke above about a metazoan common ancestor for protozoa
> >may not be as silly as it first seems. Substitute "colonial"
> >for "metazoan" and the idea begins to make sense. And what is
> >the word for multinucleate cells - many nuclei sharing a common
> >cytoplasm?
> I think both multinucleate or polynucleate are used.
>
> > It would surprise me not at all if we were to find
> >THAT morphology somewhere in our family tree.
> In fact Giardia intestinalis itself is binucleate (two nuclei) and
> polyploid. The ploidy of each nucleus cycles between 2 and 4 N.
> Whether this has anything to do with it being asexual is still
> unknown.
> William L Hunt
>
Well, that IS interesting! It suggests to me that the "sex" (which
we now suspect Giardia of practicing) may be limited to nuclear
processes - a kind of hermaphroditic selfing that doesn't involve
any commerce at all across the cytoplasmic membrane.
My implicit intuition is that modern sexual processes, involving
coordination between nuclear envelope and plasma membrane events,
originated with some purely nuclear processes. The coordination
with the plasma membrane processes came later.
Giardia may be more interesting than I thought! I have a prejudice
that parasites just cannot be primitive - even weird, early-branching
ones like Giardia. Perhaps I will have to set that prejudice aside
in this case.
Incidentally, how does one calculate Hamilton's r (IBD) for offspring
produced by selfing? It seems to me that r=1 between the parent
and offspring. The odd thing is that reproduction by mitosis and
reproduction by selfing give the same maximal value for r, even though
offspring is genetically identical to the parent in the first case,
and very different in the second case. Furthermore, two offspring
produced independently by selfing from the same parent will only
have r=0.5 between them, even though they both have r=1.0 wrt the
parent. Is that right?
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