The links between twins are exclusive and the physical similarities can surprise you. But now even more. An article published in the 'The New England Journal of Medicine' reveals that A boy and a girl, born in Brisbane, Australia, are semi-identical twins.
Each of the twins received 78 percent of their father's DNA, but the genes they have inherited from their mother are 100 percent the same. It is a third type of twins, of which only another is known in the world. But the case of the Australian brothers It is the first detected during pregnancy.
How could it happen?
"The ultrasound of the six weeks of gestation showed a single placenta and the placement of amniotic sacs indicated that the mother expected identical twins."
This is explained in the article in 'The New England Journal of Medicine' Professor Nicholas Fisk, who attended the woman and her children four years ago at the Royal Brisbane and Women's Hospital. Add that:
"An ultrasound at 14 weeks showed that the twins were a boy and a girl, which is not possible in identical twins."
It is the first time that this rare phenomenon is discovered during pregnancy. In fact, according to the Scimex news portal (Breaking Science News for Australia & New Zealand), scientists are surprised, since embryos with the characteristics of these Australian brothers often survive us.
But let's better understand the differences between identical, non-identical and 'semi-identical' twins.
A third type of twins
He has always distinguished himself between these groups of twins:
- Identical twins or monozygotic are born when a single egg, fertilized by a single sperm, divides and forms two babies.
These brothers are the same sex and share the same genes and physical characteristics.
- The non identical twins or dizygotic (known as twins). They are those that result from the fertilization of two separate ovules, each of them with a different sperm, and develop in the uterus at the same time.
They can be the same sex or different sexes and are no more similar than any brother or sister, despite being born together.
In Babies and more Twins and twins, are they the same? - In the case of semi-identical or dizygotic twinsIt is believed that the ovule was fertilized simultaneously by two sperm cells before being divided, obtaining three sets of chromosomes, instead of the usual two: one from the mother and two from the father.
And, according to the researchers, three sets of chromosomes are "practically incompatible with life and embryos do not usually survive."
Before 2007, the very idea of a third category 'sesquizigóticos' was only a theory, until the discovery by chance of twins born in the United States that turned out to be genetic copies.
Twins are more frequent
Non-identical twins are more common, due to the delay in maternity age: older women are more likely to release more than one egg during ovulation. In addition, IVF treatments usually implant more than one embryo in the mother's womb.
Having identical twins, however, is somewhat fortuitous, since it is not transmitted in the family, as in the case of twins.
But identical twins, boy and girl, sesquizigóticos, are even more strange, according to Professor Fisk, when analyzing the databases of twins from all over the world. Among the 968 non-identical twins, his team found no other cases like Australia's.
Therefore, it ensures that: "We know that this is an exceptional case of semi-identical twins."
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