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?
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.
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
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
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
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