TWIN RESOURCES

Identical or Fraternal?  For many twins, that is the question!  Whether you want to know the answer to this question with 99% accuracy from a clinical zygosity test, or are just curious to know what type of zygosities are out there, look no further!

Most people know that there are identical twins and fraternal twins, but do they really know the differences between the two?  Do you know that there could be a third type of twin?  Identical or monozygotic twins are formed when a single fertilized egg splits into two eggs.  Fraternal or dizygotic twins form when two eggs are fertilized by two separate sperm.  The third type half-identical, or polar body twins, occur when a single unfertilized egg splits before fertilization and is then fertilized by separate sperm.  

Here are some facts about identical, fraternal and half-identical twins:

Identical Twins:

• Only one-third of all twins are identical.

• Contrary to popular belief, identical twins do not “run in the family.”  No hereditary influence for identical twinning has yet been identified.

• May have one shared placenta, two separate placentas or two placentas fused into one.

• They share 100% of their genetic markers.

• Are always the same sex.

• Have the same blood type.

• Not caused by fertility treatments or maternal age.

• Can result in conjoined twins or mirror image twins.

Mirror Image, Identical Twins:

• Only about 25% of identical twins and 1% of the people in the entire world are mirror image twins.

• Mirror-image twins occur when a single egg divides later in development than typical identical twins - although the egg is still very small when it splits it already has a right side and left side.

• Mirror-image twins even as babies may display opposite behaviors/developments.

• Many times their first teeth come in oppositely and their fingerprints are mirror images as well.

• In rare cases one twin has internal organs on the usual side and the other twin has them on the opposite side.

 
Fraternal Twins:

• Can be hereditary on the mother’s side.  The tendency to hyper-ovulate, or release more than one egg in a cycle is a genetic trait that can be passed from mother to daughter.

• May have two separate placentas or two placentas fused into one.

• Share about 50% of their genetic markers, or the same as singleton siblings.  

• May be same sex or male/female.

• May or may not have the same blood type.

• Can be attributed to fertility treatments or advanced maternal age.

Half-Identical Twins:

• It is not known what percentage of twins is half-identical.

• Might have two separate placentas or two placentas fused into one.

• Share about 75% of their genetic markers, more than fraternal but less than identical.

• May be same sex or male/female.

• May or may not have the same blood type.

Here is a list of companies who conduct zygosity testing and can determine whether you and your twin are identical or fraternal.  The MATR does not necessarily endorse any of these companies- we are simply providing some examples of companies who provide this service.  Please feel free to choose the company you determine to best suit your needs.

Company	DNA Diagnostics Center (DDC)	Proactive Genetics	Affiliated Genetics
Location	Ohio	Massachusetts	Utah
Website	www.dnacenter.com	www.proactivegenetics.com	www.affiliatedgenetics.com
Phone No	1-800-613-5768	1-781-639-5126	1-800-362-5559
DNA Sample	Amniotic (CBS or amnio), blood, umbilical, cheek cell	Cheek cell	Cheek cell
Turn Around Time	3 working days	10 working days	10 working days
*Cost before shipping and handling	Starts @ $400 for legal-quality testing Also offer home-collection kits not advertised on their website.  Call them for more information.	$160 per pair	$150 per pair
Discount	$100 off Call or email the MATR for the discount code before placing your order	$20 off Call or email the MATR for the discount code before placing your order