Twins…Are They Exactly the Same?

Posted in Class Connection
cropped
Photo by Diane Arbus (via Elinar on Flickr)

by Rachael

There are two types of twins that can be formed; identical and fraternal. Identical twins are formed during the first two weeks of growth. It happens when one egg is fertilized by a sperm and splits in two. After nine months of being in the womb the identical babies are born. Identical twins share the same gender and similar phenotypes.

Fraternal twins are formed when two eggs become fertilized by two different sperm. However, fraternal twins share some phenotypes, but can have different ones too. These twins can be girls, boys, or one of each.

What makes twins so interesting is their DNA. In ordinary siblings and fraternal twins, each child receives a different mixture of two pairs of twenty-three genes from the mother and father. This is why you may have your mothers eyes and your fathers height, but your sibling could have the opposite. In identical twins, each child receives the exact same genes from each parent.

Scientist have been trying to discover if our DNA not only determines our phenotype, but also our personality. Scientists think that there is a middle to this hypothesis. That our genes can help determine different character traits, but our environment we grow up also affects us too. Identical twins are a perfect example to test this hypothesis out. If genes determined everything about us then you would concluded identical twins to be exactly the same. Despite their similar phenotypes identical twins have their own unique identities. Studying twins can allow scientist to discover what makes us the same and what makes us all different.

Questions:

1. Do identical and fraternal twins have the same fingerprints?

2. Do you know any twins? If so, do they act alike or different?

3. How common is it to be able to produce twins?

Question for picture:

1. What are some similarities and differences between these identical twins?

6 Responses to “Twins…Are They Exactly the Same?”

  1. Ryan D. Says:February 18th, 2009 at 11:05 am Rachael,First of all great post! I thinks twins, identical and fraternal are very interesting. In the picture, the girls are dressed the same way. Also they look like they have the same eye color and they have the same hair color and style. Their facial structures look almost exactly the same. They are also around the same height. Some differences that i noticed is the one twin is smiling and one is not smiling as big or not smiling at all. The girl on the right has a happier facial expression, while the one on the left has a sad facial expression. Also the one on the left looks to be some what heavier.
  2. Connor D Says:
    February 18th, 2009 at 1:19 pm Rachael,

    It was a good idea to bring up twins in this blog. I have noticed that twins tend to not act the same as each other, in both identical and fraternal, because they want to be unique. They could have their phenotype develop to become different than the other twin by means of a different diet, environment, and past illnesses. Although they are born with the same DNA, they will not grow up to be the same people because the DNA will gradually mutate in only a few years.

  3. Jennifer Says:
    February 18th, 2009 at 1:51 pm Only one set of twins in every 40,000 is conjoined, and only 1% survives beyond their first year. Abigail and Brittany Hensel are almost nineteen years old, and look like a two-headed person. They have different personalities and look almost exactly alike. They each have control of one side of their body. They each have a heart, stomach, and set of lungs, but share things from the liver and intestines down. Here is a youtube video and an article about them:

    http://www.youtube.com/watch?v=BkKWApOAG2g

    http://www.dailymail.co.uk/femail/article-425736/Abigail-Brittany-Hensel-extraordinary-bond.html

  4. Erik Says:
    February 18th, 2009 at 3:40 pm This is a really cool subject because it dives into the world of “what determines personality”. In 1979 a study was started at the University of Minnesota psychologist by Thomas Bouchard and his colleagues. they recorded the lives of some 60 identical twins who had been raised apart and scarcely met. incredibly enough the twins likeness to each other was often incredibly alike! one pair had been adopted separately at one month old, and yet they shared many common interests, got headaches at the same time of day and even shared certain habits. Another pair who were also separated at an extremely young age went on to live EXTREMELY different lives. Both were born in Trinidad but one moved to Germany and became a Hitler youth, the other moved with his family to the Caribbean, was raised as a Jew, and even lived in Israel for a time. Yet much later in life when they met they shared many traits from speech patterns to favorite foods.

    Another study was done to compare IQ among twins and came out to show that identical twins were about 85% similar while Fraternal are about 60%. This raises a ton of debate about whether “smarts” are an inherited trait, or due to surrounding environment as well as other personality traits. Some scientist believe that if basic needs are met such as food, shelter, and parental care, genes are the primary mechanisms for determining personality. Some stick to the belief that personality is largely environment based.

    Many scientists have also discovered genes that seem to be linked with certain personality traits as well. Its some really fascinating stuff that raises the question “what is it that makes me me?”

    here is a link to the Washington post site about all of this http://www.washingtonpost.com/wp-srv/national/longterm/twins/twins2.htm

  5. Rachael Says:
    February 19th, 2009 at 10:22 pm Wow, thanks for adding new information! Erik and Jennifer your comments were really interesting and provided so much more information for my blog. I am answering my own question though, “Do twins, identical and fraternal have the same fingerprints?” My hypothesis was that fraternal twins would not have the same fingerprints, but identical twins do. It turns out my hypothesis was wrong. Although, identical twins share the same DNA and fraternal twins share similar DNA. However, they do not share the same finger prints. This is because our fingerprints are not inherited from our mother and father. Our fingerprints are influenced by random stresses that happen in the womb. Even a slightly different umbilical cord length is able to change our fingerprint. This just proves that everybody in the world is their own unique person and no two people, even the closest identical twins are not exactly alike.

    http://www.livescience.com/mysteries/060909_twin_fingerprints.html

  6. Rachael Says:
    February 20th, 2009 at 2:53 pm Here is my interview with a biologist student, James J. Young:

    Question: Do identical twins share a more similar IQ then fraternal twins?

    Answer: Yes, identical twins generally have more similar IQs than fraternal twins.

    The heritability of IQ is 40-80%. Heritability is a measure of the

    amount of variance of a trait in a group that is determined by

    genetics as opposed to other factors. You can think of it as the

    amount that genetics pushes an individual away from the mean of the

    population.

    (IT% – FT%)*2 = Heritability

    Heritability is calculated by subtracting the percentage of identical

    twins with the same IQs (IT%) from the percentage of fraternal twins

    with the same IQs (FT%) and multiplying by two. This is because

    identical twins are 100% alike in their genes whereas fraternal twins

    are only 50%. We assume that the extra 50% of genetic-relatedness

    manifests in more similar IQ, and we can calculate its amount using

    that formula.

    Because heritability is positive — not zero — for IQ, identical

    twins have on the whole more similar IQs that fraternal twins.

    (Note that whether IQ is primarily genetic or determined by the

    environment is still a very controversial subject among scientists.

    Even though identical twins have more similar IQs than fraternal

    twins, high IQ probably also has strong environmental causes.)

    Question: Are there any cases in twins where one has been normal why the other one is mentally disabled?

    Answer: Yes. If the heritability of IQ were 100%, then the only thing that

    determined IQ would be genetics, and difference among identical twins

    would not be possible. But it isn’t. This means that environment

    plays part of the role.

    There are certainly cases where identical twins have had markedly

    different IQs, though these cases are rare. In most of them, I would

    say it happened because of a developmental problem in the womb rather

    than because of a genetic cause. For example, it would be impossible

    for one identical twin to have Down’s syndrome while the other did not

    because Down’s syndrome has a genetic cause. But mental retardation

    – using the medical definition of IQ

11 thoughts on “Twins…Are They Exactly the Same?”

  1. Rachel, this was an excellent post that captured my attention because my basketball coach has recently become pregnant with identical twin girls. The births of multiples have become increasingly more common in the United States. In the year 2000, there were 118,916 Twin Births, 6,742 Triplet Births, 506 Quadruplet Births, and 77 Quintuplets & Other Higher Order Births. About 3% of all births in the United States were of multiples. Naturally the chance of giving birth to twins is only about 1.7%. In my opinon, this increase of multiples is due to many advances in bio technology. More and more women are using fertility treatments. Fertility treatments can include fertility drugs and in vitro fertilization. This increases the chance of having twins to about 20-25%! The chance of having identical twins is significantly lower. About 1 in 250 women give birth to identical twins.
    Although it seems that the chances of giving birth to twins are very high, these statistics show that it is actually quite low. I think that the media has influenced our view of the frequency of twins. Due to the high demand of interest on this topic, there have been many documentaries and television shows that involve the births of multiples. The famous television show Jon and Kate plus 8 features two sets of multiples, fraternal twins and sextuplets. This case was extremely rare and was aided by the use of fertility drugs. Twins have become more popular due to many influences of the media.

    All of the statistics mentioned were found on: http://www.keepkidshealthy.com/twins/twin_statistics.html

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  2. Hey Rachael, 😀

    Great article!! I especially liked the videos explaining how twins are born. Another question you might want to think about is: If having twins is a hereditable trait! I did some of the research for you though and here is what I found… Being a twin does give you an increased chance of having twins, and some families have had many generations of twins. But, being a twin does not mean that you can’t give birth to a single child. Also, some doctors and scientists believe that the ability to have twins is only passed on by the mother, because the mother is the one who ovulates.

    But having a family history of giving birth to twins is not the only way that people can have twins, and it is not the only reason WHY people have twins. Some other reasons are birth control pills, fertility pills, dairy products, and if you have children at a later age you have a higher possibility to have twins.

    Due to recent TV shows and magazines having twins has become a new fad, and more twins are being born throughout the country… even though the statistics are low, it seems like twins are everywhere. More and more women a year are receiving in vitro fertilization and taking fertilization drugs. But some scientists wonder if taking these drugs and having these procedures will basically CREATE a new hereditable trait in the family to have genes. So in generations to come scientists will be watching these “created” twins to see if they will produce twins or other multiples of children.

    Here is a site that can further explain these scientists and doctors theories…. http://multiples.about.com/b/2009/07/10/forum-friday-are-twins-hereditary.htm

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  3. Hi, my name is Lucy and I have an identical twin. We are a rare kind of twin. We are monoamniotic twins, which share the same amniotic sac. We also shared the same umbilical cord, which spilt to feed both of us. We are also mirror image. Our teeth came in on opposite sides at around the same time. Our parts on on opposite sides. Although we are both right handed. My mom says that her doctor told her that there was a 50% chance that one or both of us would die before we were born. That is partly because we could have cut off one of the others blood supply if our cords got too tangled. There was no dividing membrane between us and we kicked each other in the face a lot. But both of us survived. My mom’s cousin also had monoamniotic twins. One of them has severe heart problems because their internal organs also were mirror image and her wiring is all wrong. Plus her heart didn’t form properly. She’s survived many surgeries and made it past her first year. We hope she will live a fairly normal life.

    This kind of twin is not supposed to run in families because it’s so rare. But there is an instance of this kind of twin in every generation in our family as far back as my great grandfather. Past that point there are twins, but we don’t know if they were monoamniotic or not. They seem to be identical in any case. We have a picture of my great great great grandfather and his twin brother. They look like Abraham Lincoln. So in my mom’s generation there are two cases of monoamniotic twins, in my grandfather’s generation there is one set of them and in my great-grand father’s generation there is a set of them, but one didn’t survive. They didn’t even know she was carrying twins until after the baby was born. But they know she carried a monoamniotic set of twins because they could see how the remains were attached to the umbilical cord.

    We also have chickens that just laid an egg with two yolks. I guess if that hatched, it would have been monoamniotic chicks!

    We are 11 years old and my mom homeschools us.

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  4. Let me start off by saying that i learned a lot about twins and how they come to be. I found a few more reasons of how someone is more likley to have twins. If a woman is in their 30’s or 40’s gives them more of a chance because they have higher levels of estrogen. If a woman is a twin her slef that also gives them a higher chance of haveing twins because they have that trait. The only thing i want to critisize you on is that you say identical twins are exatly the same. Since they are identical that does not mean they are the same person. Alot of the time twins do have the same friends. I also see a lot of twins that like diffrent things and have different friends. All in all good post.
    http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Twins_identical_and_fraternal

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  5. this is an interesting website i have just recently learned about twins which i am researching at the moment i wanted to ask are there any differences in twins due to only the environment?

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  6. Hi Rachael, Great Post
    As Guy said, I’ve also learned a lot about twins by reading this post, thank you. I think its interesting that women from 30-50 years old are more likely to have twins.
    I also think its interesting that out of all multiple births twins are 95% of all multiple births, even though they only come about every 90 or so births. Triplets are born every 1 out of 10,000 births, and are becoming more popular as Briana C. said, with fertility treatment. Fraternal twins are more common than identical twins, because it is more rare for a single fertilized egg to divide into to fetuses.
    This is a great site for information.

    http://pregnancyandbaby.sheknows.com/pregnancy/baby/Baby-boom–Expecting-twins-triplets-or-more-5580.htm

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  7. I am an identical twin and I have always tested higher in i.q. than my sister. She is a yard care worker and never finished university. I have a doctorate in the humanities and teach. Our personalities are, and always have been, very different. Do twins dress alike because they think alike and just naturally want to wear the same thing every day? No, nonsense. We used to fight like cats and dogs over what to wear in early childhood. Finally, my mother said “You don’t have to dress alike, you know”. What a revelation. What freedom! Based on my own experience as an identical twin, I’d say societal expectations are responsible for a lot of perceived identicalness in personalities in identical twins. I’ve read a lot of crap on identical twins along the lines of “separated at birth but, wow, they both have a cat and use the same brand of toothpaste!”. DNA aside, I’d say that two people, no matter what their outward appearance, are separate and unique on the inside. People who expect identical twins to be like clones in sci-fi movies really irk me.

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  8. Great topic for an article and I have just one note because I understand that this is a learning experience in getting properly attributed images, using images with permission as well as credible sources.

    I recognized the black and white photo of the twin girls as the work of renowned photographer Diane Arbus, though the credit line is to ‘elinar’ and is from a flickr page that has a note that this is a cropped version (smaller detail) of Diane Arbus’s photo. Would you please revise the photo credit to the original photographer (after checking permission copyright status – might be from Metropolitan Museum of Art)?

    You can see the original full-sizd photo and some other information about Diane Arbus here:
    http://en.wikipedia.org/wiki/Diane_Arbus

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  9. My sister and I are 16 year old identical twins. Reading through comments here, it surprises how little people know what I thought to be common knowledge about twins.. ha.

    When I was younger and used to frequent forums, it seemed like everyone was vehemently aware that “twins are different! they don’t have to be the same!” and they’d act angry at the seeming perception that twins were the same.. except there wasn’t really anyone on that side anyway. I also grew up hearing that twins fought a lot. Hmm..

    As for my sister and I, we are pretty similar. We share food preferences, aesthetic tastes, social views, etc. Gradually, however, we’ve grown to look more different over the years (because of mutations, probably), and slightly different temperaments. I have no complex over our similarity; it only makes sense. If not for the originally identical genes, we’ve at least shared the same upbringing, environment, and so on.

    The main bothersome thing about “societal expectations” is the whole image of mysticism. I get questions about telepathy etc. My twin and I don’t share telepathy, although we understand each other very well because we’ve grown up together. I can understand why people would wonder, but seriously? Try not to shove your corny ESP ideas onto me just because I have a biological copy :/

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  10. Il semblerait que même les jumeaux identiques ne seraient pas identiques au niveau du génome. Dù moins c’est ce que prétend un chercheur de l’Université Western Ontario, Shiva M. Singh dans:

    Ontogenetic De Novo Copy Number Variations (CNVs) as a Source of Genetic Individuality: Studies on Two Families with MZD Twins for Schizophrenia

    Guillaume Girard, biologiste

    http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0017125

    http://www.montrealgazette.com/health/Scientist+discovers+twins+identical+even+they+look+alike/4532673/story.html#ixzz1IZFwhEk8

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