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Are We Identical?
It might seem obvious
in most cases that two siblings are identical just by looking at
them, but in cases where they have slight differences in appearances
it may be necessary for a DNA test.
Twin Zygosity
Identical or
monozygotic twins will have an exact DNA profile. When the sperm met
the egg, the zygote (baby to be) split and formed two embryos.
Because the DNA contributed by the parents came from the same sperm
and egg, the two children inherit the same DNA. With fraternal or
dizygotic twins, the mother releases two or more eggs that can be
fertilized by separate sperm giving them different DNA profiles.
Fraternal twins are related in the same way as siblings. (see
science of paternity)
What can a twin
zygosity tell me?
An exact matching
profile between two siblings is so unlikely to occur out of random
chance that it can be concluded that an exact match confirms the
identical twin relationship. In the event that the mother is unsure
whether the two children are from the same father even though they
were born together, we can perform a sibling test in conjunction
with the twin zygosity at no extra charge.
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