6 Types of Twins That Are Extremely Rare

What is the main difference between identical and fraternal twins?

• Identical twins develop from two separate eggs, while fraternal twins develop from one egg.

• Identical twins develop from one fertilized egg that splits, while fraternal twins develop from two separate fertilized eggs.

• Identical twins always share a placenta, while fraternal twins always have separate placentas.

• Identical twins are always the same gender, while fraternal twins are always different genders.

What is a characteristic feature of mirror image twins?

• They have completely different DNA.

• Their internal organs are always on the same side of their bodies.

• They are physical mirror images of each other, sometimes with organs on opposite sides.

• They are always born with a shared placenta.

According to the fission theory, what causes conjoined twins?

• Two separate embryos fuse together during development.

• A single fertilized egg splits very late in development, but incompletely.

• Genetic mutations cause the twins to develop abnormally.

• Environmental factors during pregnancy lead to physical attachment.

What is a potential benefit of studying external heteropagus twins?

• Understanding how human cells develop.

• Learning about the behavior of animal cells.

• Discovering new types of twins.

• Preventing all twin pregnancies.

What is one theory about what a "fetus in fetu" actually is?

• A type of identical twin that develops outside the womb.

• A highly developed tumor made of various body tissues.

• A twin that completely disappears during early development.

• A twin that is absorbed by the mother's body.

What is a characteristic of chimeric twins?

• They are always identical twins.

• They have cells from two different individuals within their body.

• They are born with extra limbs.

• They are unable to have children.

What makes sesquizygotic twins unique compared to identical or fraternal twins?

• They are always conjoined at birth.

• They share exactly 25% of their DNA.

• They share between 50% and 100% of their DNA.

• They are formed from two separate eggs fertilized by one sperm.