<%@LANGUAGE="JAVASCRIPT" CODEPAGE="1252"%> DoubleTake Not Identical or Fraternal Twins
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NOT IDENTICAL OR FRATERNAL BUT STILL TWINS

SOURCE: LA Times, April, 2, 2007 (from April issue of the journal, Human Genetics)

Doctors have identified a third type of twins - somewhere between identical and fraternal - after performing extensive genetic test on two children.

They are refering to the pair of "semi-identical" - two sperm cells fused with a single egg - and said this was a previously unknown way for twins to arise.

With fraternal twins, the most common type, the mother contriubtes two eggs that each are fertilized in the womb by two different sperm cells from the father. They are genetically as similar as ordinary siblings.

With identical twins, one egg from the mother is fertilized by one sperm from the father, and then very early in developent the embryo splits and two fetuses grow. These twins are very similar genetically.

The new case came to light because one of the twins had abmbiguous genitalia and was considered a hermaphrodite, with both ovarian and testicular tissue. This child is being raised as a girl. The other twin is a boy.

Writing in the April issue of the journal, Human Genetics, researchers said: "This observation suggests the existence of other similar twins that have not et been, and may never be, identified.

 

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