Second-Ever Case of Semi-Identical Twins Identified

Bhutanese twins Nima and Dawa will take their first steps in public as separated girls when they leave a leading Melbourne pediatric hospital on Monday

Bhutanese twins Nima and Dawa will take their first steps in public as separated girls when they leave a leading Melbourne pediatric hospital on Monday

This extremely rare phenomena is the result of two sperm fertilising the same egg. "However, an ultrasound at 14 weeks showed the twins were male and female, which is not possible for identical twins", Fisk added. According to a press statement about the research, the twins are only the second set of semi-identical twins ever reported in the world, and the very first set to be identified while still in utero.

Doctors in Australia say they have discovered a rare set of twins who are neither fraternal nor identical, but something in between.

It suggests that such twins are incredibly rare, as embryos such as these often do not survive.

Identical twins occur when cells from a single egg fertilised by a single sperm split into two, sharing identical DNA. "Some of the cells contain the chromosomes from the first sperm while the remaining cells contain chromosomes from the second sperm, resulting in the twins sharing only a proportion rather (than) 100 percent of the same paternal DNA". When the doctors examined the girl twin's ovaries, they found some changes linked to cancer, and so "the hard decision was made to remove them so she didn't develop cancer", he said.

USA Today reports the first set of semi-identical twins were reported in the U.S.in 2007. In that case, the twins were studied by doctors in infancy after one of them appeared to have ambiguous genitalia.

Nearly all twins are either fraternal - in which two eggs and two sperm create two separate embryos, or identical - in which one embryo is fertilised by one sperm and splits into two embryos.

Sesquizygotic represents a third type of "twinning" between identical and fraternal. It's this odd place in between, ' Dr Gabbett said. They are the product of just one egg and one sperm, which originally form one embryo, but which break into two during the earliest stages of pregnancy. A baby's sex is determined by sperm that carry either an X or Y chromosome; generally speaking, females have two X chromosomes (XX) and males have an X and a Y chromosome (XY). Professor Fisk, a past President of the International Fetal Medicine and Surgery Society, worked alongside clinical geneticist Dr Gabbett.

Though we may not see another set of semi-identical twins like this any time soon, Doctor Gabbett says that it's good to acknowledge incredible cases like that of these Queensland twins.

This, according to Queensland University of Technology scientists, is "typically incompatible with life", the BBC reports, and embryos which result from the process usually don't develop into babies. On investigation of mixed chromosomes, doctors found the boy and girl were identical on their mother's side but shared around half of their paternal DNA.

These twins will be the same sex and share the same genes and physical features.

After studying the two amniotic sacs, the medical team was able to determine the twins were sesquizygotic, which occurs when one egg is fertilized by two sperm at the same time.

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