Identical twins can differ
 Q: I would like to know if my twin boys could be identical if one is
allergic to cow milk but the other one is not? They each had their own sac
but the sacs were fused together when they were born. They told us the
twins had a 25% chance of being identical. --Bea F.
A: Identical twins with separate placentas are the ones that are most nearly
identical, says Harvey Kliman, M.D., PhD. at the Yale University School of
Medicine. Doctors often, however, mistakenly identify them as fraternal.
Kliman suggests: look at your twins. If their appearance is almost identical,
they probably are identical.
[Michael Tucker, IVF.com] The developing embryo hatches and may split
into twins
Allergies depend on the environment and an intolerance level within the body
that builds during a person's lifetime. One twin's level may have triggered
early.
Even identical twins can have biological differences. Identical twins do have the same genes but never the same mitochondria (which also
contain genetic material). The mitochondria split into two different sets at the very first division of the fertilized egg-before twinning
occurs.
Such differences can cause identical twins to be different. In the case of Kliman's identical twin girls, "...one LOVES broccoli, the other
HATES it."
* * *
Note: Mitochondria are tiny sacs--so small you need an electron microscope to see them--elongated, like a sausage. Many bop around in each heart, pancreas,
or kidney cell. Their job is to burn food and produce energy. Mitochondria have their own genes, separate from the genes inside each cell's nucleus. These
genes come only from the mother.
(Answered by April Holladay, science correspondent, Mar. 6, 2002)
Further Surfing:
USATODAY.com, WonderQuest: How eggs split to form twins
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