Sex chromosomes have been in the tidings a lot recently thanks to conjecture about Olympic athletes , but a Modern discovery show how far we are from translate how exactly they forge . In particular , the determination demonstrate that the animal kingdom has found a diverseness of ways around a vital problem sex selection would otherwise pose for wellness .
Humans , like most mammals , use an XY sex selection system where – in most cases – females have two X chromosomes and males have an disco biscuit and a Y. Even ignoring the cases thatbreak this design , this beat a biological challenge when it developed . The disco biscuit chromosome carries far more factor than the Y , many of which are n’t sex - specific . If both Xs were full expressed , female mammals would get a double dose of the proteins these genes code for , with disastrous consequences .
Almost 40 years ago , co - source of the studyProfessor Jenny Gravesof La Trobe University regain mice and mankind with XX chromosomes avoid this throughnon - product of the mRNAthat computer code for these genes . One disco biscuit chromosome is “ silenced ” as a solution . Consequently , they get the same sexually transmitted disease of ten chromosome - coded proteins as those with XY chromosomes . “ As the cistron were silenced by their unsuccessful person to make RNA , the control of dose recompense was assumed to be at the level of RNA only — not at the level of making proteins , ” Graves say in astatement .
When studies showed hens and rooster have unequal storey of mRNA from their sexual practice chromosome , it was assumed that they would have similarly unmatched protein , and perhaps matching protein stage were not so important . Now , inquiry shows that chickens do have methods to compensate so their protein back breaker match – they just do it other than .
Moreover , this is not a simple split between birds and mammal ; theplatypususes the same method as poulet , despite very different chromosome .
Chickens , like other birds and some reptilian , have a ZW sex selection system . Here , it is males that have two copy of the same chromosome , the Z , while females have a Z and a W. Nevertheless , the likely trouble are the same – a risk of protein doubling , although this time in male hiss .
Previous workhad shown that wimp do not silence one entire izzard chromosome the way humans do with an X. Instead , still come on a factor - by - gene basis . More puzzlingly , however , investigator have now designate that disregarding of mRNA production , manly and female chickens produce the same level of protein , other than where needed for reproduction .
This had not been noticed previously because , somewhat amazingly to non - biologists , it ’s much easy to track the amount of messenger RNA in a jail cell than the ensue protein level . “ Proteins are complicated , ” Graves told IFLScience . “ RNA is fairly gentle to measure these day , we can get a good readout on how much there is in a cell . ” Nevertheless , protein measurements have improved recently to the detail other members of the team were able-bodied to do the necessary chicken checks .
“ The findings suggest that dose recompense is a of the essence process in species with differentiated sex chromosomes to ensure that protein levels are balanced , ” said Dr Paul Waters of the University of New South Wales in the statement .
The work also proves that recompense can occur either when transcribe messenger RNA or when translating to protein , and both can be compound , as chickens have done .
Although most mammals use silencing at the written text level , rather than when it come up to protein output , previous research carbon monoxide - authored by Gravesdemonstratedplacental mammalian and pouched mammal have train different but overlapping methods to reach this silencing .
The new subject area elaborate the mammalian picture further , showing that platypus also partly overproduce mRNA from their repeat chromosome , but balance this with blue protein production . platypus have sex option chromosomes that areas strange as they are . Instead of either XX or XY chromosome , male have five of each , while females have five pairs of Xs , all of which need to line up .
Graf told IFLScience she suspects the common ancestors of chickens and platypus similarly balanced their dosage partly at the transcription level and partly at transformation . However , she admits no other bird coinage have been test in this way so far , so further complications may arise . The composition notes evidence of variation among reptiles . Komodo dragonsdo not appear to reduce recording of their ezed chromosomes at all , while thegreen anole(which uses XY chromosome ) does all the dose recompense at transcription , like us .
The fashion most mammals do it ; “ Is probably more efficient , ” Graves tell IFLScience , but there could be benefits to the flexibility of mix and matching . She ’s intrigued that the ballock - laying platypus uses the same method as birds , and wonders if shut up at arrangement is particularly applicable for unrecorded births .
Failing to dose compensate is not always disastrous . Graves told IFLScience that in one still experimentation , it was found that ; “ Only about ten percent of the genes are dose sensitive . ” However , there can be disastrous consequences from that ten percent if protein output does duplicate , including failure to form certain bones .
grave tell IFLScience that the discovery that there are other ways to achieve dosage recompense could also be relevant for case where a non - sex chromosome is double up , most famously in Down Syndrome .
Moreover , Graves noted ; “ X chromosome inactivation is the model for epigenetic silencing that is affected by environmental circumstances . We always think it was at the transcriptional level , but mayhap not . ” With contamination and stress sometimes make undesirable gene - silencing , expert knowledge of how this can occur might have valuable outcome .
The study is release open access inProceedings of the National Academy of Sciences .
