Why do twins and triplets look alike?

From Issue: Discovery 6/01/2011

Dear Alyssa,

Terrific question. First, the reason that some twins and triplets look alike is because they have identical DNA. DNAis the blueprint that tells the body how to build itself. In the case of “identical” twins, one fertilized egg splits into two, and each “half” becomes a twin. In the case of “identical” triplets, one of those halves then splits in two again and becomes a twin of a twin. The reason I put the word “identical” in quotation marks is because even though they have the same DNA, there are things about them that are different. Sometimes their height and weight are different, and even their fingerprints are different. These differences occur because of factors in their environments and other things. For instance, one may like to eat more than the other, and that might cause that twin to be taller or weigh more. Also, it is important to know that not all twins are “identical.” Some twins are called “fraternal” twins. Fraternal twins do not share the same DNA. In that case, one can be a boy and the other a girl. They develop just like typical children and are not “halves” of the same egg, but are from different eggs. Isn’t it amazing how God designed humans to be able to have twins or triplets, or even more? And yet all those people are unique and precious in His sight.


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