An anonymous pair of Australian-born twins have been dubbed as sesquizygotic, a term that refers to their condition of being somewhere between identical and fraternal. To differentiate the three terms, identical twins are those that come from the same egg but split into two, thus having identical genetic material. Fraternal twins are also called non-identical twins wherein two separate eggs were fertilized simultaneously. Now, the distinction for semi-identical twins is explained thus:
Here’s how doctors think this remarkable event happened: They suspect that a single egg cell from the mother was fertilized by two sperm cells, and then it divided in an unusual way, forming two embryos that developed as semi-identical twin babies — one male and one female. The twins share 100 percent of the DNA from their mother, but only 78 percent of the DNA from their father. As a result, these twins share a very rare 89 percent of their DNA. Meanwhile, identical twins share 100 percent of their DNA, and fraternal twins share 50 percent of their DNA (the same amount as ordinary siblings). The Australian twins lie in between the two.
(Image credit: Jens Johnsson/Unsplash)
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