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From: B. Harris)
Subject: Re: Quick biology question
Date: 25 Jun 1998 03:03:38 GMT

In <6mr719$jk2$> writes:

>>  It would be impossible to tell
>> which of the male twins fathered (or mothered - except for the obvious
>> ;-)) any particular child. This could be an interesting situation in
>> the case of family conflicts, as there is know way you could say to one
>> of the fathers, "This is your brother's child, not yours." Same DNA
>> profiles.

   And the same child as if it had been the brother.  Indeed, somewhere
I read of a testicular transplant from one identical twin to another.
Later, the transplantee fathered a child.  Suppose he'd done it by
artificial insemination?  Would it be any different than if they'd used
sperm from the twin?

>This seems to be more than a mundane question, too. Suppose one twin
>commits a murder and leaves some genetic material behind. The twin could
>have a very good chance of casting a shadow of a doubt by saying, "My
>twin has the same DNA fingerprint. He (she) has no solid alibi at the
>time of the murder." Etc. I suppose that's a United States sort of
>problem, but you see what I mean.

   A case like that was actually in the news not long ago.  The DNA was
the same, so far as sequence went, but the chemical structure of the
hair was not.  Due to the fact that the twins had been eating slightly
different diets, their body hairs had slightly different and
distinctive stable isotope ratios (C-12/C-14 and N-14/N-15 etc).  They
nailed the murderer that way.

                                       Steve Harris, M.D.

From: B. Harris)
Subject: Re: Question about Twins
Date: Sun, 27 Jul 1997

In <5renri$pqj$> (dic) writes:

>Can someone please tell me whether identical twins have the same DNA structure
>and fingerprints? If so, what quantitative method can be used to tell them

   They have the same DNA, but not the same fingerprints or retinal
patterns.  DNA doesn't have enough information to tell where every cell
goes, and is more of a recipe than a blueprint.  Twins are not exactly
alike for much the same reason that two chocolate chip cookies from the
same batch are not exactly alike.

                                      Steve Harris, M.D.

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