Identical or fraternal twins?

They are so similar... but are they really the same? Today we are going to speak about the difference between identical and fraternal twins.

First of all, a twin is one of two offspring in the same pregnancy. The main difference between identical and fraternal twins is that identical twins come from the same zygote that is divided in two different embryos, and fraternal twins come from two different zygotes fertilized by two different sperm cells.

Twin differences. Picture from www.genomesunzipper.org

Ok, until now it seems easy, more or less. But in real life, what can make us differentiate between both types of twins? Here some clues:

Slight differences

Let's start with general genetics: "What is DNA and what is for?" and "How could we be apparently so different among us but at the same time the same species?"

For answering the first question we will start with the Central Dogma of Molecular Biology:

The DNA is our particular library, essential for life. We have all the necessary information encoded in a combination of four nucleotides (A, T, G and C). This library has hundreds of books, which we are going to call RNA. We have a lot of different kinds of RNA, which maybe is boring and not what you are looking for at this blog. So let's say that this RNA should be translated into proteins to be useful for a cell. These proteins will work independently or as a subunit of a big complex to make what is required.