Tom Matthews tmatth at
Fri Feb 20 00:43:46 EST 1998

Jim Cummins wrote:
> In article <34EBE78E.3066 at>,Tom Matthews <tmatth at> wrote:
> > I will assume that you mean identical twins rather that fraternal twins
> > which are merely brothers.
> >
> > Even identical twins, however, are of at least two kinds. All share
> > original nuclear DNA, but some may have different mitochondrial DNA.
> Tom is this documented?  I presume this is due to random segregation of
> mutant genotypes? I'd appreciate a reference as I'm currenly writing up a
> review of mtDNA inheritance in relation to fertility and infertility.

See my other reply for my reasoning. I did some hunting on medline and
found quite at lot about discordance of monozygotic twins, but nothing
definitive about them possibly having different mtDNA, although the
possibility was actually tested in several papers.

However, I also found the following abstract which suggests a
redistribution of cyoplasmic constituents during separation can also
lead to monozygotic discordance.

Acta Genet Med Gemellol (Roma) 1975;24(3-4):251-259 
[Possible role of the cytoplasm in the course of morphogenesis, namely,
in the case of twinning].
[Article in French] 
Giroud A

A number of facts that cannot be interpreted in terms of nuclear genes
would seem to be interpretable in terms of cytoplasmic heredity. The
hereditary role of the mitochondria has already been demonstrated in
molds. The role of the cytoplasm (matrilineal heredity) has also been
shown in some phanerogams, and analogous facts have been noted in
insects and molluscs. In amphibians, the influence of an alteration of
the egg cortical cytoplasm has been shown to reappear in the following
generations. This cortical cytoplasm includes the morphological plan of
the organism with its bilateral symmetry. In Tatusia novemcincta the
twins may be morphologically or chemically different, which may only be
explained by an unequal subdivision of a heterogenic cytoplasm. Similar
facts are observed in human twinning. Monozygotic twins are usually
discordant with respect to congenital malformations (especially symmelia
and anencephaly), which may only be interpreted in terms of unequal
distribution of cytoplasmic properties. 

Tom Matthews
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