In order to reach these findings, though, the team started by comparing various genomes of species from multiple organisms, looking for similarities. The genomes selected were from eukaryotes; prokaryotes -- organisms like bacteria that contain no cell nucleus; vertebrates -- organisms with a spine; invertebrates -- organisms without a spine, such as insects; vascular plants -- plants that can transport food and material throughout their tissue; and unicellular organisms.
From there the team looked specifically at the chromosomes of 68 random eukaryote genomes. This amounted to observing 886 chromosomes, 22 of which were human autosomes -- any chromosome other than a sex chromosome. The sex chromosomes of each species were omitted because of their vastly different evolutionary history from other chromosomes, Yu said.
The researchers placed each fully sequenced eukaryote genome onto an X-Y axis, hoping to find similarities between the various organisms. To help generalize the vast amount of information, the X-Y axis graph was standardized with each species.
"It eliminated a scale effect and made it possible to compare a species with several dozen chromosomes to a species with much fewer chromosomes," said Xianran Li, research associate in agronomy.
That's when the team noticed the shockingly consistent distribution pattern.
"We could not believe this the first time the plot was generated," said Chengsong Zhu, research associate in agronomy.
The only genomes that deviated from forming an S-curve were that of the platypus -- an organism that contains characteristics of birds, reptiles, mammals, amphibians and fish -- and those of birds. Birds are unique because in addition to their usual chromosome sequences, they contain one additional set of minichromosome sequences, according to Zhongwei Lin, res
|Contact: Jianming Yu|
Kansas State University