What is the Difference Between Fraternal and Identical Twins?

Tricia Christensen
Tricia Christensen
Because identical twins developed from one pair of ova and sperm, they are genetically indetical.
Because identical twins developed from one pair of ova and sperm, they are genetically indetical.

Fraternal and identical twins have many differences. Identical twins are often described as those children resulting from a pregnancy that are identical to each other. Actually, more than resemblance is involved, and not all identical twins look “completely” alike, though they do share many of the same physical characteristics. As they age, they will have differences based on lifestyle choices, experiences, and a variety of other factors. Fraternal twins, though sharing a womb, have fewer commonalities, and both types of twins are most identified by how they begin life.

Twin-to-twin transfusion syndrome affects 15 percent of identical twin pregnancies.
Twin-to-twin transfusion syndrome affects 15 percent of identical twin pregnancies.

Most commonly, the way twins first begin life can be referred to as dizygotic and monozygotic. Dizygotic, or fraternal twins, result when a woman has two ova or eggs fertilized by two separate sperm. This can mean that fraternal twins are of different or the same gender. Though they are siblings, they do not share near identical genetic material.

Fraternal twins are sometimes one boy and one girl.
Fraternal twins are sometimes one boy and one girl.

Within each sperm or ova, there is variance in what gets inherited and expressed, and these children are as alike as siblings, which can be very alike or unlike. They also may share a special relationship because they shared a womb. Though these twins are the same age, however, they are usually easily distinguished from each other, just as it would be simple to tell apart siblings of different ages.

Identical twins don't always look exactly alike.
Identical twins don't always look exactly alike.

The conception of monozygotic (identical) twins is very different. Instead of two separate ova being fertilized by two sperm, these twins begin as one ova and one sperm. During the early process where the fertilized egg begins to produce more cells, it doubles itself and creates two embryos or two babies, instead of one. Since both babies are produced from the same fertilized egg, they share almost all the same chromosomes and DNA structure, and will bear remarkable resemblance to each other. They are truly more related than fraternal twins because of their beginning.

Researchers estimate that roughly 90% of all twins are fraternal.
Researchers estimate that roughly 90% of all twins are fraternal.

There are other differences between fraternal and identical twins. Identical twins are much more rare, and only 8% of all twins are identical. Moreover, fraternal twinning can be hereditary, but identical twinning is seldom hereditary and occurs with the same general likelihood in all populations.

There is much greater difference in the number of fraternal twins born in various populations, suggesting a degree of inheritance. Fraternal twinning is not always the product of genetics. Multiple births are less common in women who are vegetarians, and much more likely when women undergo fertility treatments to conceive.

Not matter how twins begin life, they will all have differences. Choices in life can make significant impact on which DNA gets expressed. This means identical twins will evolve along separate paths, though many of them stay very close. Most child development experts believe that both identical and fraternal twins should be encouraged to celebrate their individuality, since considering them as the same does not give each twin the opportunity to find his or her own gifts and strengths.

Tricia Christensen
Tricia Christensen

Tricia has a Literature degree from Sonoma State University and has been a frequent contributor for many years. She is especially passionate about reading and writing, although her other interests include medicine, art, film, history, politics, ethics, and religion. Tricia lives in Northern California and is currently working on her first novel.

Tricia Christensen
Tricia Christensen

Tricia has a Literature degree from Sonoma State University and has been a frequent contributor for many years. She is especially passionate about reading and writing, although her other interests include medicine, art, film, history, politics, ethics, and religion. Tricia lives in Northern California and is currently working on her first novel.

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Discussion Comments

anon955864

Identical twins do not always look identical. In about 99.9 percent of cases they do. Most people do not know, however, that there are cases, a few cases, only twelve recorded cases of Male/Female identical twins.

This happens when a male, from a male/male set, 'mutates' if you would, during development into a female.

Out of these twelve cases, only two have been reported that the female did not develop Turner's Syndrome.

I know this simply because my sister and I are one of the pairs out of twelve.

burcidi

I know that identical twins will have different personalities, but I still think that they are more similar to one another in terms of personality than fraternal twins.

I have both identical twins and fraternal twins in my friend group. The fraternal twins are nothing like each other. They have totally opposite personalities and like different things.

The identical twin boys, on the other hand, are fairly similar. They enjoy many of the same hobbies, have lots of mutual friends and spend time together.

fBoyle

@ankara-- A good way to remember the difference between identical and fraternal twins is to keep in mind that identical twins come from one egg and one sperm and fraternal twins come from two eggs and two sperm.

Identical twins will always be the same gender, because the second embryo is simply a copy of the first. So everything will be exactly the same.

With fraternal twins, the embryos are fertilized by separate eggs and separate sperm. So if the genetic material determining gender are different, they will be of different sex.

Fraternal twins are simply two unique babies growing together at the same time in the womb. Identical twins is the same embryo splitting into two, resulting in two babies of the same DNA makeup and characteristics.

bluedolphin

I know that fraternal twins can be of different genders. But identical twins are always of the same gender right? Why is this?

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    • Because identical twins developed from one pair of ova and sperm, they are genetically indetical.
      Because identical twins developed from one pair of ova and sperm, they are genetically indetical.
    • Twin-to-twin transfusion syndrome affects 15 percent of identical twin pregnancies.
      Twin-to-twin transfusion syndrome affects 15 percent of identical twin pregnancies.
    • Fraternal twins are sometimes one boy and one girl.
      Fraternal twins are sometimes one boy and one girl.
    • Identical twins don't always look exactly alike.
      Identical twins don't always look exactly alike.
    • Researchers estimate that roughly 90% of all twins are fraternal.
      Researchers estimate that roughly 90% of all twins are fraternal.