At first , everything seemed normal for one 28 - yr - old mother who was fraught for the first time in Brisbane , Australia . An ultrasonography at six week revealed a modest but common surprise : a undivided placenta and two amniotic sacs . She was fraught with identical twins .
Eight week later , however , a follow - up ultrasound exposed a much more prominent origin story . The identical twins were a son and a young lady – an inconceivable discovery for counterpart with a shared placenta .
" We could seevery clearlythat they appeared to be very similitude from very early on in the pregnancy , so it issue forth as quite a blow to laterdiscoverthat one was a boy and the other a girl , " Dr Michael Gabbett , clinical geneticist at Queensland University of Technology ( QUT ) , narrate IFLScience .
To investigate further , the doctors performed genetic testing of the amniotic fluid in each sac . The tests let out the twins are identical in some respects but not in others . The boy and girl divvy up 100 pct of their female parent ’s DNA , but only about 50 percent of their forefather ’s , resulting in 78 percent shared genetic information .
The unique couple are only the 2nd semi - identical pair known . This means they are not monozygotic ( identical ) or dizygotic ( fraternal ) but “ sesquizygotic " ( semi - identical ) . The uncovering is described inThe New England Journal of Medicine .
So how did this genetic mashup happen ?
The semi - selfsame similitude are a sesquizygotic cross between superposable and fraternal duad . Identical twins lead from a single sperm fertilizing a sole egg , with the prison cell later dividing in two . These individual share 100 percent of their desoxyribonucleic acid .
brotherly twins spring up when two eggs are fertilized by different sperm , each becoming a decided conceptus . These twins have a separate placenta but share a womb , finish up with about 50 percent similar DNA , just like non - twin siblings .
The sesquizygotic twins are an “ exceptional average ” . They are genetically identical with respect to their mother but differ by 50 per centum in the DNA they inherited from their Padre . The aesculapian team dubbed this “ a third frame of twinning . ”
The Brisbane twins are likely the result of one egg being fertilize by two sperm cells , resulting in three chromosome . These three chromosomes were equally divided into two Bunche of prison cell that then became two embryos . Years later , the fetus are now 4 - year - old bambino . Phew , what a appendage !
The twins were return by cesarean section and had normalApgar scores , a quick judgement of newborn infant in the min after birth . Due to aesculapian complication , the young young lady had her correct limb amputated at 4 weeks of age . At 3 years , she was also diagnosed with gonadal dysgenesis , a inborn developmental disorder that meant her ovaries had to be removed .
“ Otherwise , both twins [ are ] developmentally normal , ” wrote the authors .
Is this a rare consequence ?
Yes , it seems so . This is only the second - known time semi - superposable twins have been recorded . The first werereportedin 2007 – they too are indistinguishable on their mother ’s side but fraternal on their sire ’s side . However , these kids were not identified as semi - superposable until years later , when one was noted to have ambiguous privates , with both ovarian and testicular tissue . The other was anatomically male . They too appear to be doing well and growing commonly .
" The received precept is that when an bollock cell is fertilize by two sperm cells , the baby receives three curing of chromosomes , " saidDr Gabbett . " We do see this occasionally in maternity and rarely in newborns however these babe usually die ahead of time on in the maternity . What this research demonstrates is that it is possible for nature to adjust this issue so that the pregnancy can exist and result in relatively respectable , developmentally normal children . "
Does this mean ourcurrentclassification of similitude is oversimplify ?
