'Extraordinarily Rare' Semi-Identical Twins Were Born in Australia.

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A pair of twins born in 2014 shared all of their mother's genes, but only 78 percent of their father's. It all started when two sperm fertilized an egg at the exact same time.
Credit: QUT
▼ Twins can be fraternal, identical — and in extremely rare cases — semi-identical.
A pair of twins born in January 2014 in Australia share all of their mother's genes, but only 78 percent of their father's, according to a new case report published yesterday (Feb. 27) in The New England  Journal of Medicine.
It's unclear how many other semi-identical, or "sesquizygotic," twins are out there, but it's likely "extraordinarily rare," said lead author Dr. Michael Gabbett, the diagnostic genomics course coordinator at the Institute of Health and Biomedical Innovation in Brisbane, Australia. The first set of semi-identical twins was identified in 2007 in the U.S., when they were infants; this is the first time semi-identical twins have been identified in the womb, according to the report.
Initially, the mother of the twins described in the case report thought that she was pregnant with identical twins, based on an ultrasoundearly in her pregnancy. Later in the pregnancy, however, the woman's doctors were surprised to see that the twins were a boy and a girl. Because identical twinsshare all of their genes, they can't be of opposite sexes like fraternal twins can.
To analyze the fetuses' genes, the doctors took samples of the amniotic fluid that surrounded each twin. (The twins were in separate amniotic sacs in the womb.) This was how they found out that the twins shared 100 percent of their mother's genes but only 78 percent of their father's.
Normally, a human's DNA comes from two sources: one set of chromosomescomes from the mother's egg and one set comes from the father's sperm. In fraternal twins, two sperm fertilize two separate eggs, yielding twins that share half of their mother’s genes and half of their fathers; in identical twins one sperm fertilizes a single egg, which splits up into the twins that share all of their mother and father’s genes. But in the semi-identical twins, one set of chromosomes came from the egg, and the second set was made up of chromosomes from two separate sperm, Gabbett told Live Science.
But how does this happen? (▪ ▪ ▪)

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adwitiya.ankita

In anthropology we did study about twin... I also get this information from that field. But it is so nice of you to share it in this forum to inform everyone.. thank you sir