Identical Twins Don’t Share 100% of Their DNA

We get half of our DNA from our mother and half from our father. This DNA comes in packages called chromosomes. Most people have 46 chromosomes arranged in 23 pairs. When we get our DNA from our parents, we inherit one chromosome from each of their pairs. Now that the DNA lesson is over, what about twins? Identical twins form from the same egg and the same genetic material from their parents, but that doesn’t mean they’re genetically identical. That’s because identical twins pick up genetic mutations in the womb, as their cells weave new strands of DNA and then split into more and more cells. Even though twins share a significant amount of similar DNA, there are clear genetic mutations between each member, proving that they are not carbon copies of each other. What about the children of twins? Since they both have the same DNA, it’s almost like the two sets of children have the same mothers but different fathers. In fact, this is why at the DNA level they’re more like half-siblings instead of first cousins. That’s because they share 25% of their DNA, instead of the usual 12.5%. Imagine the confusion when identical twin sisters marry identical twin brothers.