In Queensland, Australia, babies were born, which are of the rarest semi-identical type. This is only the second officially recorded case in the history of mankind. And the first one that is found through genetic testing.
Usually in humans, one sperm fertilizes one egg, but if the second is lucky, then the output is two embryos, two organisms, whose DNA coincides by 50%. In another, less common case, a fertilized egg can split into two copies of itself, and then identical twins will appear, whose DNA is 100% identical. But if two spermatozoa fertilize one egg, then semi-identical twins are obtained, in which the maternal part of the DNA is the same, and the paternal part is different.
This case is interesting in that the special condition of the twins was determined even before birth. When the ultrasound showed two amniotic sacs in the same placenta, it became clear that these were identical twins. But re-examination after 8 weeks showed that it was a boy and a girl, which is nonsense. A version about semi-identical children arose and samples were taken to check it - the genetic analysis confirmed everything. These babies are only 89% the same.
As a rule, if two sperm enter the egg, a cocktail of a triple set of chromosomes is obtained, which is not viable. Add to this the natural defense mechanism of the egg, which allows only one sperm to pass through, and it turns out that the birth of such twins is an event of unprecedented rarity. To avoid undue misdirection, doctors keep the details of these children confidential.