At 22:06 16/03/97 -0000, you wrote:
>On Sun, 16 Mar 1997, Gerard Tromp wrote:
>>> Timothy Sutter wrote:
>> > [...]
>> > Identical twins are like diasteriomers i.e. "mirror images."
>> > A clone would be achiral, meaning the clone would be truly identical.
>>>> Perhaps you would like to clarify as to how you view identical twins as
>> diastereomers. Last time I looked 'situs inversus' was not particularly
>> more common among identical twins than among the broad population.
>> (Situs inversus is the condition in which the internal organs occurr in
>> a mirror image fashion, i.e. heart angled more toward right, liver on
>> the left etc. That is, internal organs appear as if in mirror image.)
If I recall accurately, identical twins are desended from one fetilised egg
(a zygote) which cleaves abnormally at some stage to give two embryos.
Perhaps Timothy was thinking about the geometry of this atypical cleavage
event. I think that the geometry of the cleavage event would not produce
'mirror images' (except in the case of situs invertus') as the cells are
totipotent at the time and left and right may have no meaning...further,
directionality may only be turned on later after gastrulation by external
factors (think of which 'side' implants into the wall of the uterus)
>> Due to reasons of mitochondrial donors noted below, identical twins
>> will be more alike than clones unless the clone nucleus and egg donor
>> are the same individual. Identical twins share all genetic material,
>> nuclear and mitochondrial, identically.
>>A little speculation here: all mitochondria in a cell are not the same. i
agree that their DNA sequence is identical initially, however the rate of
mutation of each mitochondrial genome is different, for unknown
reasons.Thus, if you had a zygote with 10 mitochondria, 4 may be normal, 4
may be functional normal (with silent or consevative mutations), 2 may be
nonfunctional. In the twinning event, would each twin get one nonfunctional
mito. or would Tweedledum get the two 'bad' mitos and Tweedledee get no
'bad' mitos?
does anyone know?/have any ideas?
Richard Kerr.
The Murdoch Institute,
R.C.H. Flemington Rd, Parkville, 3052,
AUSTRALIA.
kerrr at cryptic.rch.unimelb.edu.au
Phone (61) 3 9345 5045.
