Difference Between Identical Twins and Fraternal Twins (With Table)

Twins are two children born from the same pregnancy. Monozygotic (‘identical’) or dizygotic (‘non-identical’ or ‘fraternal’) twins exist. One fertilized egg splits and develops into two newborns with identical genetic information, resulting in identical or monozygotic twins. Two eggs are fertilized by two sperm to produce two genetically distinct infants in fraternal or dizygotic twins.

Identical Twins vs Fraternal Twins

The difference between identical twins and fraternal twins is that, to form identical twins, one fertilized egg splits and develops two babies with the same genetic information. Fraternal, or dizygotic, twins, on the other hand, are the outcome of the fertilization of two different eggs during the same pregnancy. Fraternal twins might be of different sexes or the same.

Monozygotic twins are identical twins who share the same DNA. They are caused by the fertilization of a single egg with a single sperm, which then separates in two during embryonic development or cell division. Identical twins have the same sex and share all of their DNA.

When two separate eggs are fertilized by two sperm, fraternal twins, also known as dizygotic twins, result. The term “dizygotic” refers to the zygote, which is the fertilized egg that will develop into an embryo and grow into a kid. Fraternal twins make up the bulk of twins.

Comparison Table Between Identical Twins and Fraternal Twins

Parameters of Comparison Identical Twins  Fraternal Twins  
  Development  The same egg divides into two halves.  Fertilization occurred with two separate sperm cells and two different eggs.  
Sex of the twinAlways share the same sex.  Usually different sex.  
DNA  Have the same DNA.Do not have the same DNA.  
Blood TypeAlways the same.  It may or may not be the same.    
  Causes  Not known.  Certain fertility drugs, Hereditary predisposition, IVF.  
  Physical similarities  Stunningly similar, however, due to environmental factors, they may not be exact duplicates.  As similar as any other sibling.  

What are Identical Twins?

When a single egg is fertilized, it produces one zygote (thus the term “monozygotic”), which subsequently divides into two separate embryos. Monozygotic twins are more likely created when a blast cyst includes two inner cell masses, each of which will lead to a different fetus, rather than when the embryo splits when hatching from the zona pellucida, according to a recent theory.

Embryo splitting can be used to make monozygotic twins artificially. It can be used to enhance the number of available embryos for embryo transfer by expanding in vitro fertilization (IVF). Unless a mutation occurs during development, monozygotic twins are genetically nearly identical and usually of the same sex. Monozygotic twins’ children test as half-siblings, not first cousins, genetically.

Monozygotic twins are not genetically identical, despite their close genetic resemblance. The DNA of 66 pairs of monozygotic twins’ white blood cells was examined for 506,786 single-nucleotide polymorphisms found in human populations. Identical twins indeed have the same DNA code as one another. This is because identical twins are made out of the same sperm and egg from their father and mother.

What are Fraternal Twins?

Fraternal twins are also called dizygotic twins. Fraternal and identical twins are distinguished by the fact that fraternal twins are produced from two distinct eggs. Fraternal twins can be of the same gender and share many of the same qualities, but they can also be completely different. Fraternal twins are similar to each other but not identical to one other.

Boy-girl twins are the most common dizygotic twins, accounting for half of all cases. The second most common occurrence is girl-girl twins. Boy-boy twins are the rarest type of twin. Fraternal twins, like brothers and sisters, will share around half of their genetic makeup. They share around half of their DNA, just like any other siblings. Because both individuals inherit half of their DNA from Mother’s egg and a half from Father’s sperm, the two kids will share some characteristics.

Many factors that influence multiple births have little effect on fraternal twinning. Only dizygotic multiples are affected by heredity, birth control pills, and diet, which can all reduce a woman’s chances of generating multiples. This is because all of these circumstances may promote hyperovulation, which results in the production of more than one egg per cycle, increasing the odds of conceiving twins.

Main Differences Between Identical Twins and Fraternal Twins

  1. One fertilized egg separates into two newborns with the same genetic information, resulting in identical or monozygotic twins. Fraternal or dizygotic twins, on the other hand, are formed when two eggs are fertilized by two sperm and two genetically distinct children are produced.
  2. Identical twins are nearly identical. On the other hand, like any other sibling, fraternal twins are not identical.
  3. Identical twins pretty much always have the same blood type. On the other hand, fraternal twins may have the same or different blood groups.
  4. Identical twins share all of their genes and are always of the same sex. While fraternal twins share half of their genes, they can be of the same or different sexes.
  5. Identical twins have the same DNA. While fraternal twins do not have the same DNA.


Identical or fraternal twins with separate placentas are possible. For health reasons, it’s critical to determine if your twins are identical or fraternal. A genetic test can be requested after the infants are delivered to determine if they are identical or fraternal twins. The zygosity test is the term for this procedure. This non-painful test involves covering the inside cheeks with a soft applicator and collecting samples of baby cheek cells.

If one of a pair of identical twins is diagnosed with a disease, the other twin should be closely followed for early signs of illness. Multiple births have become more prevalent in recent years as more couples turn to fertility medicines and IVF treatments to help them conceive. Approximately 3% of live births in the United States are twins.


  1. https://psycnet.apa.org/record/1953-07072-000
  2. https://jamanetwork.com/journals/jamapsychiatry/article-abstract/491444
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