Identical twins form when a single fertilized
egg splits into two genetically identical parts. The twins share
the same DNA because they were originally from the same fertilized
egg. Because identical twins share exactly the same DNA, they
will often look very similar. However, environmental factors
also play a role in development and sometimes, identical twins
may look very different even though they have exactly the same
DNA. Identical twins are always the same sex.
What is a Fraternal Twin (dizygotic
twin)?
Fraternal twins develop from two completely
different eggs which are fertilized by two different sperm.
The genetic connection of fraternal twins is no more or less
the same as siblings which are born at separate times. Fraternal
twins may be the same or different sexes, and they may look
similar to each other or they may look very different.
