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The oldest known sex chromosome in brute has been bring out , push back the date for the development of sexuality chromosome to between 248 million and 455 million years ago .
The ancient chromosome was found inoctopusand calamari , suggesting that these may have been among the first animals to determine their sex via hereditary blueprint , instead of environmental cues .
Octopus and squid appear to have evolved sex chromosomes at least 248 million years ago.
Sex chromosome are standard in mammal . In humans , the sex chromosomes are X and Y. Males usually have an X and a Y chromosome , while females have two Xs , although there are some variations , such as XXX or XXY , which can have a wide ambit of shock from no burden at all to certain learning disabilities or neurologic differences .
For a long time , researchers were n’t sure whether cephalopod mollusk , the soft - bodied mollusks that admit squid and octopus , determine their sexual practice with chromosomes . mollusk have a change of way to handle replica , including hermaphroditism or sequential hermaphroditism , in which person swap sexual activity over time .
Octopuses stick to one sexual activity , but it was n’t decipherable whether genes or environmental cues determined what sexual urge that would be . In some reptiles and fish , factors like temperature settle the sexual urge of offspring .
Researchers discovered the chromosome after completing the full gene sequence of the California two-spot octopus.
come to : Octopuses torment and eat themselves after mating . scientific discipline finally know why .
In 2015 , researchers finish the first full factor sequence of a cephalopodan , the California two - spot octopus ( Octopus bimaculoides ) . That sequence still include gaps , though , so a squad lead byAndrew Kern , a biologist at the University of Oregon , limit about filling them in with high - fidelity sequence .
They presently noticed that one chromosome , chromosome 17 , seemed less filled - out with genes than the other chromosomes in their chronological sequence . Because they had sequenced a female octopus , they compare their results to the earlier individual , a male . In the case of the male , chromosome 17 look no less populated than other chromosomes in the octopus .
This was a clue that chromosome 17 might have something to do with gender differences . To confirm , the team sequenced four more octopuses , two male person and two female , and confirm that females have just one copy of chromosome 17 , while male have two . Thus , they map the devilfish sex chromosomes not as XY and XX as in human race , but as ZZ and Z0 .
The researcher then compared their devilfish genomes to the genomes of three other octopus specie , three species of squid , and the chambered nautilus ( Nautilus pompilius ) .
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They found the ZZ / Z0 pattern in the calamary and the octopus , but not in the nautilus , a more distantly related species . This show that the sexual urge chromosomes evolve after the split between the nautilus line and the logical argument leading to modern calamary and octopus , which pass off between 455 million and 248 million years ago .
" This is an astoundingly long sentence for a sex chromosome to be preserved , " the research worker wrote in their paper , which is now available pre - peer critique on the preprint websiteBioArxiv .
Prior to this research , the oldest confirm gender chromosome was in sturgeon fish , according toNature News , with an long time of about 180 million years .
