DNA Testing

Twin DNA testing

DNA testing can be used to determine whether twins are identical or not.  Besides being a really interesting fact to know, there are also medical implications as to whether a twin is a true identical twin or just a really similar looking fraternal twin.

As I’m sure you know, there are two types of twins—identical twins and non-identical twins.  The scientific terms for these two types are maternal and fraternal twins.

A little background on these.  There are two ways that a woman can become pregnant with twins, and these two ways are completely different. 

Fraternal Twins

Ovulation is the process of the woman's body ejecting an egg into the fallopian tubes, where it is ready to be fertilized. Sometimes when a woman ovulates, two egg cells are ejected into the fallopian tubes instead of one. 

Whether this happens or not is dependant on the woman’s own genetic makeup, so if a woman doesn’t have fraternal (non-identical) twins in her family, she probably will not have her own (although fertility treatments can also result in multiple egg ovulation, resulting in fraternal twins, triplets, or (gasp!) even more!).  If both egg cells are fertilized, she’s going to have twins. 

These twins are known as fraternal twins.  Since they come from two different sperm cells as well as two different egg cells, they will have completely different DNA, as different as two siblings who aren’t twins.  They also develop in two different birth sacs.

Maternal Twins

Maternal twins, or identical twins, on the other hand, begin as one fertilized egg.  A fertilized egg is essentially a single cell, which divides into two, and those two into four, until a fully grown baby is formed.  Sometimes, the after original cell splits in two, those two cells break off from each other, resulting in two independent identical cells.  These cells each develop into a full grown baby, and they develop in the same birth sac.  These babies will have the exact same DNA patterns, as they each started as the same fertilized egg.

This can occur to anyone, regardless of genetic makeup of the mother, as identical twins are, essentially, a "freak occurrence" of sorts.

In many cases fraternal twins can look very similar, as can any two siblings, but in the case of fraternal twins the resemblance is apt to be even more striking because the two children are the same age.  Additionally, maternal or identical twins can look different—there are factors that are not determined by DNA, such as the shape of one’s nose.

DNA testing can easily determine whether twins are fraternal or maternal, by testing to see if their DNA is identical or not. Keep in mind, though, that this test is also not 100% accurate, because not the entire DNA pattern is tested.

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