|How can twins look so different?|
|Question Date: 2018-10-16|
There are two kinds of twins. One kind has the
same set of DNA. These are called “identical
twins,” even though they might not be quite
identical. These twins started out as one
fertilized egg, but the embryo split in two early
on when the embryo only had about 16 cells.
The other type of twins are called
“fraternal twins.” They are as genetically
alike as any other pair of siblings (brothers
and/or sisters). They started out as two separate
We expect identical twins to be pretty similar
and their looks and behavior, but they will have
differences. That’s because our environment
shapes us too. Our environment starts before
we’re even born. People can also make a lot of
decisions that affect how they look and behave.
One twin might even choose to make those
differences great. For example, if one twin likes
sports and short hair, the other twin might focus
on art and grow their hair long because they want
to be seen as an individual, not as part of a pair
Scientists find it very useful to study
identical twins that were raised apart or compare
identical twins with fraternal twins to try to
figure out which of our characteristics are
determined more by genetics and which are
determined more by environment. Which
traits do you think fall into each of those
Thanks for asking,
I first want to make clear that there are two
types of twins, identical and fraternal.
Detailed discussions of the
two and their
differences can be found on
ScienceLine already. For this question,
which seems to assume identical twins, know that
at birth identical twins have the same DNA while
fraternal twins have only half of their DNA in
common. For fraternal twins, the answer to this
question is relatively straightforward:
differences in appearance are due primarily to
the differences in DNA.
Fraternal twins are as similar to each
other as any other set of siblings with similar
variance in their traits (
phenotype ). For identical twins, other
factors must be dominating. Notice the
specification that the DNA of identical twins is
the same only at birth (and even then, it is
probably perfectly identical). DNA is not as
static as is sometimes implied;
our DNA and the
parts of it that we use can
change as we age.
Differences in environment
life experiences also contribute to
changes in appearance.
If one twin goes outside and gets more sun
than the other, the pair may have some difference
in skin color and aging; differences in
diet will affect height and weight;
illnesses, exercise habits, and a
plethora of other factors also contribute. I'd
also like to point out that these effects of
environment do not change the appearances only of
identical twins; they happen to everyone, but
identical siblings are the only group which gives
us a "baseline" for comparison.
I am not sure what you mean by 'so different'.
Twins are children by the same parents, but there
is no reason why they have to be anything more
than that. There are identical twins, who are
clones of each-other, but if not identical, then
there is no reason why twins would be any more
similar than two non-twin children of the same
Some twins happen in their mother when one
embryo divides into 2 identical embryos, and
identical twins are born.
Some twins happen in their mother when 2 of the
mother's eggs are fertilized with 2 different
sperm, and 'fraternal' twins are born.
They look like siblings of each other, but they're
That is a good question! In fact, there are
actually two “types” of twins!
Monozygotic twins are sometimes called
“identical twins,” and they are born
when a single egg is fertilized by a single sperm
to form a single zygote, which
divides into two embryos. This means that they
share 100% of the same DNA,
and as a result look almost identical.
On the other hand, dizygotic twins, which are
sometimes called “fraternal twins”
are born when two eggs are fertilized by two
different sperm. This means that
they do not share 100% of the same DNA, and that
is why they can look
different from each other.
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