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Get Educated Twin Style: Learn the Different Types of Twins


You may already know the two main types of twins: identical and fraternal. But if you dig a little deeper, you’ll find there are many rare types of twins, which do not always get the same attention.

In reality, new types of twins are being discovered periodically and new advancements in medicine, social studies and science often center on twins and multiples.

If you’re raising twins, or around twins, learning which type of twin you are interacting with is a valuable insight. Now you will not only have powerful knowledge at your disposal, but also have an awesome party trick; naming all thirteen types of twins.

 

 Twin 101

 

Let’s start with the birds and the bees–how twins are made. The two main types of twins are identical and fraternal. But new studies suggest that we’re just scratching the surface on the different kinds of twins.

Most common

 

identical twins1. Identical twins (monozygotic):

Come from one egg that splits and forms two embryos. They share DNA and often identical finger prints. Identical twins do not have to look alike. I know it’s shocking, but true. They will however often share a placenta.
1. One Egg

2. One Sperm

3. Egg Splits

 

 

fraternal twins2. Fraternal twins (dizygotic):

 

Develop from two eggs and forms into two embryos. They have different DNA and different finger prints. Fraternal twins can look identical, but still be dizygotic. Usually fraternal twins come from two placentas.
1. Two Eggs

2. Two Sperm

 

Rare twins

 

conjoined twins

3. Conjoined Twins (monozygotic):

 

Are twins that do not fully separate from each other. This is caused by the incomplete division of the fertilized egg. Connection could happen at different points of their body even sharing tissue, organs or limbs.
1. One Egg

2. One Sperm

3. Incomplete division of the Egg

 

twins conceived separately4. Twins Conceived Separately (Superfetation):

 

After an egg is fertilized, another egg might be released resulting in twins that are conceived at different times and different days.

1. One Egg Released

2. Fertilized by Sperm

3. Another Egg released

4. Fertilized by Sperm

 

 

Twins with Different Fathers5. Twins with Different Fathers (Heteropaternal Superfecundation:

 

This is when two separate eggs are released at different times and are fertilized by two separate conceptions. Basically, superfecundation happens when a mother has two separate encounters with two different partners.
1. One Egg Released

2. One Sperm from one man

3. One Egg Released

4. One Sperm from another man

 

"Half Identical" Twins6. “Half Identical” Twins (Polar Body Twins):

 

This happens when an egg splits and then each half is fertilized by a sperm. Resulting in Identical twins who are biologically identical, coming from the same placenta, but aren’t a 100% DNA match, fraternal.
1. One Egg splits

2. Each half meets a sperm

 

 

 

Boy/Girl Identical (Monozygotic) Twins7. Boy/Girl Identical (Monozygotic) Twins:

 

This is when a male twin loses their Y chromosome and then develops into a female. The female twin would be afflicted with Turner’s Syndrome, characterized by a short build and no ovarian development.
1. One Egg

2. One Sperm

3. One Male twin loses Y chromosome

4. Becomes Female with Turner’s Syndrome

 

Mirror Image Twins (monozygotic)8. Mirror Image Twins (Monozygotic):

 

Happens when a fertilized egg splits more than a week after conception. Resulting in twins that have reverse features and look like a reflection of one another; mirror image. For example, one might be left handed while the other right handed.
1. One Egg

2. One Sperm

3. Egg Splits late

 

Parasitic Twins9. Parasitic Twins (Monozygotic):

 

When a healthy twin has a smaller twin inside their body or externally attached. In both scenarios, the smaller and weaker twin is directly connected to the blood supply of the stronger twin. Often if it is an internal twin it may not be discovered until adulthood.
1. One Egg

2. One Sperm

3. Incomplete division of Egg

 

 

 

Semi-Identical Twins10. Semi-Identical Twins:

 

One twin is a hermaphrodite with both testis and ovaries, while the other is anatomically male or female. This happens when two sperm fertilize one single egg, which then splits.
1. One Egg

2. Two Sperm

3. Then Egg splits

 

 

Twins with Different Birthdays11. Twins with Different Birthdays:

 

This can happen in three ways; first the labor begins before midnight with one twin being born before 12AM and the other is born the next day. Second one twin is born on New Year’s Eve and the other New Year’s Day. They could have different birthdays, in different months and years. Third, the pregnancy is delayed after the first birth. This is commonly used with premature twins. One twin is healthier and the other is weaker and must stay in the womb longer.
1. One Egg

2. One Sperm

3. Egg Splits

0r

1. Two Eggs

2. Two Sperm

 

Twins of Different Races12. Twins of Different Races (Dizygotic):

 

This can be caused by lab mix during in-vitro or fraternal twins which have two different races. Meaning the eggs could be more than one race and the sperm as well. This creates a separate genetic combination in each egg.
1. Two Eggs

2. Two Sperm

 

Multiples13. Multiples (more than two):

 

Most commonly results from in-vitro, rarely natural conception, and can have a combination of identical and fraternal twins. Two could be identical while the rest fraternal. Or it could be sets of identical pairs with one being a fraternal pair. The combinations are endless.
1. One Egg

2. One Sperm

3. Egg Splits

0r

1. Two Eggs

2. Two Sperm

 

Information from: Top 10 Unique and Unusual Types of Twins. By Pamela Prindle Fierro

 

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This article was written by Twinologist

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