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A twin zygosity test is a DNA test that is performed
on twins and which definitively shows whether twins
are identical or fraternal.
When twins are born, the physician usually is able
to tell whether twins are identical or fraternal by
examining the placenta. Identical twins usually
share a placenta, while fraternal twins are usually
in two different placentas.
However, sometimes records can be lost, the
placentas might have been discarded or damaged
before twin zygosity was determined, or doubt may
arise because of the twins’ physical
characteristics. In such cases, only a DNA test will
be able to reveal the truth. A twin zygosity test
compares the twins’ DNA profiles to see whether they
match—an exact match proves that the twins are
identical.
The results of a twin zygosity test may be used to
satisfy personal curiosity as well as to help solve
health problems for the twins later down the road.
For example, in the event that a twin needs an organ
or tissue transplant donor, the identical twin is a
perfect choice.
Identical vs.
Fraternal Twins
Identical twins come from one fertilized egg,
called a zygote. The zygote, which usually develops
into one child, grows and splits early in
development to form two embryos—identical twins.
Because the twins come from one egg and one sperm,
they have exactly the same DNA.
Fraternal twins, on the other hand, develop
when there are two different eggs in the mother’s
womb that are fertilized by two different sperms.
Fraternal twins will not have exactly the same DNA,
although like other siblings, they can be expected
to share some of the DNA they inherit from both
parents. |
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