Birds and reptile hold some of their factor in microchromosomes so small they were once thought to be detritus on the microscope sliding board . A comparative work across many species has found most wench have been maintain similar microchromosomes since before their ancestors had spines , let alone wings . Meanwhile , the same bits of DNA have join average chromosomes in mammalian , except theplatypus , which is doing its own affair , as usual .
Human chromosomes hold back close to 3 billion al-Qaeda pairs of DNA , with lengths of around 3 to 6 µm ( 0.00012 - 0.00024 inches ) . Birds and reptiles have a low telephone number of similar - sized macrochromosomes , along with 30 - 32 microchromosomes about a tenth as long .
AProceedings of the National Academy of Sciencespaper reveals the microchromosomes in a crybaby are similar to those in an Amphioxus , a sort of gutless deep - ocean wight that diverged from the vertebrate crinkle 684 million long time ago . Most other doll have kept the same solidifying of microchromosomes as well , the paper reveals , with a few odd exception like eagles and some parrots .
“ We lined up these sequences from birds , turtle , snakes and lizards , Ornithorhynchus anatinus and human being and equate them,”Professor Jenny Gravesof La Trobe University said in astatement . “ Astonishingly , the microchromosomes were the same across all bird and reptilian species . Even more astonishingly , they were the same as the bantam chromosome of Amphioxus . ”
Graves and co - authors were able-bodied to describe bequest of a few microchromosomes in patch of human chromosomes , but most mammals have absorbed and scrambled the microchromosomes so good they seem like any other bits of DNA . “ The exception is the Ornithorhynchus anatinus genome , in which the microchomosomes have all fused together into a few large blocks , ” Graves said .
Graves told IFLScience the platypus almost for certain served as a stepping stone to the mammalian approach to chromosomes , a leg the earliest mammalian went through , but only monotremes have maintained
Microchromosomes are productive in genes for their size , the paper notes , containing less non - coding “ junk DNA ” than macrochromosomes . There also seems to be no figure as to the function of microchromosome genes . However , knowing this beforehand did n’t make Graves any less surprised to key out how well some metal money have preserved them at the same time as genes have shuffled between chromosomes in others .
tomb told IFLScience geneticist have spent 50 years debate whether there is an evolutionary benefit to coalesce DNA into large chromosomes or splitting it up . “ For cistron that work together well it may help to have them on the same chromosome , ” Graves explained , but in most cases , the fusion or nuclear fission may ruminate the invasion oftransposable elements , often fromold viruses , with no evolutionary welfare or harm .
However , Graves admitted to IFLScience she does not understand how electric cell move a mix of large and little chromosomes around when bird cellular phone need to replicate . “ I do n’t imagine we have think hard enough about the auto-mechanic of puzzle both into the daughter cellular phone . ”
Another mystery is how the shift relates to the constitution of new species . What happens when an animal with gobs of microchromosomes mates with one with only the great version ? “ That ’s a really deep question , ” Graves differentiate IFLScience , and geneticist have been puzzling over interchangeable topics since the 1930s . “ I suspect when you have a major chromosome alteration in a population young do n’t do so well , you have gametes with too many of some cistron and too few of others . ” How this does n’t obturate the process of forming new coinage , no one knows .
