Multiples: From Twins to Octuplets and Everything In-Between!

I just read an interesting article by AC producer, Michelle L. Devon (Michy) entitled, Are Identical Twins Really Identical? I have always been fascinated with multiples, especially identical multiples, so I did some research and found some very interesting information.

Recently, geneticists in the United States discovered a set of twins unlike any other twins medical science has ever seen. They call them them 'semi-identical twins'. This type of twin is so rare that it is possible they may be unique.

It appears that two sperm cells must have fertilized a single egg and each twin has DNA from each of the two separate sperm cells. While this does happen occasionally, it's only in about one percent of all human conceptions. Then, in most cases, the embryo is not viable. For a 'semi-identical twin' to form, this fertilized embryo then must split to form twins. Then, after all this has happened and the babies are born, something has to occur to get the attention of the geneticists. In this case, what got their attention was that one of the babies was born a true hermaphrodite, having both testicular and ovarian tissue. The other twin is a normal male infant. Neither twin has other physical or mental developmental abnormalities and they are now healthy two year olds.

I've always been especially fascinated with triplets and have often wondered about identical triplets. Triplets are rare enough, with 'spontaneous' triplets appearing in only about 1 in 8100 births; but Identical triplets are extremely rare, occurring about once in every 500,000 births. Triplets born from fertility treatments are never identical because with fertility intervention, individual eggs are used for zygotes (a cell that is the result of fertilization). To produce Identical triplets a single zygote must split into three.