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Twins can be fraternal , selfsame — and in extremely rare cases — semi - identical .
A pair of twins born in January 2014 in Australia share all of their female parent ’s genes , but only 78 percent of their father ’s , according to a new case study published yesterday ( Feb. 27 ) inThe New England Journal of Medicine .
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.
It ’s unclear how many other semi - selfsame , or " sesquizygotic , " twins are out there , but it ’s likely " extraordinarily rare , " said lead story source Dr. Michael Gabbett , the symptomatic genomics line coordinator at the Institute of Health and Biomedical Innovation in Brisbane , Australia . Thefirst curing of semi - identical twinswas distinguish in 2007 in the U.S. , when they were infants ; this is the first time semi - monovular twins have been distinguish in the uterus , concord to the account . [ see two-fold : 8 Fascinating Facts About Twins ]
Initially , the mother of the twins key in the face report thought that she was pregnant with superposable twins , base on anultrasoundearly in her maternity . Later in the pregnancy , however , the fair sex ’s MD were surprised to see that the twins were a boy and a miss . Becauseidentical twinsshare all of their gene , they ca n’t be of paired sex like fraternal twins can .
To analyze the fetuses ' factor , the medico took sample of the amnic fluid that surrounded each twin . ( The twins were in separateamniotic sacs in the uterus . ) This was how they found out that the twin deal 100 pct of their mother ’s gene but only 78 percent of their founding father ’s .
commonly , a human ’s DNA amount from two informant : one set ofchromosomescomes from the female parent ’s egg and one set comes from the father ’s sperm cell . In fraternal Twin , two spermatozoon fertilize two freestanding eggs , give twins that deal one-half of their mother ’s genes and one-half of their father ; in identical twin one sperm fertilizes a unmarried eggs , which splits up into the Twin Falls that share all of their mother and father ’s genes . But in the semi - identical twins , one set of chromosome come from the testis , and the second exercise set was made up of chromosomes from two freestanding sperm , Gabbett told Live Science .
But how does this go on ? Gabbett hypothesizes that the mother’segg was fertilizedby two disjoined sperm cell , each post its own hardening of chromosomes – – one stage set of chromosomes from the female parent end up combining with two unlike sets of chromosomes from the father .
Once an egg is fertilise , it becomes impenetrable to other sperm , so Gabbett believe that the two spermatozoon must have arrived at the bollock at the same prison term . Any other account , such as two sperm cell fertilizing two nut with the exact same genic makeup , " is biologically implausible , " he added .
Next , the three sets of chromosome would ’ve been divvied up into three separate cells : One cell received chromosomes from the mother and first sperm cell , the other from the female parent and 2nd sperm cell and the third from both sperm cells . Because a cellphone needs chromosomes from both the mother and founding father to survive , that last one would have finally died . The surviving cells would go on to merge together and then divide again into the two twins .
In summation , the girl and boy each havemale and distaff sex chromosome — in other parole , each twin has some cells that carry an XX pair ( female ) and some that pack an XY pair ( male person ) . experience both manly and female pairs of sex chromosome throughout various cells in the body is link to certain developmental problems in thereproductive organsas well as Crab , Gabbett say . When the doctors try out the young lady twin ’s ovaries , they found some changeslinked to cancer , and so " the unmanageable decision was made to withdraw them so she did n’t break Crab , " he order .
The girl also developed a blood clot before long after she was born — blood clotsare a coarse tortuousness for identical Twin Falls in general — and the clot cut down off the blood provision to her branch . As a result , Dr. also had to amputate her branch .
There is safe news , however : The twins are now 4 and a half years old and are otherwise germinate normally , Gabbett said .
To get a well agreement of how uncommon sesquizygosis counterpart are , the researchers went on to analyze the genes of most 1,000 other twins and did n’t find another case of semi - identical twins , nor did they find grounds of the term in a late study from another research team that examined DNA from more than 20,000 twins .
Still , it ’s potential that there are causa physician have missed : Unless the twins are different genders , sesquizygotic twins could be lose , because people might just assume they ’re indistinguishable twins , Gabbett said . Even so , we " believe this is so rarefied thatroutine testingis not justify , " Gabbett said .
Only one other case in the humanity has been report , to their knowledge , Gabbett said . Because of its curio , " some doctors still do n’t believe that it exist . "
Originally published onLive Science .
