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Mycoplasma | || Genome Size in bp Gram positive bacteria | a Gram negative bacteria i Fungi / Moulds Algae Worms Crustaceans Echinoderms nsects Mollusks Birds Bony fish Cartilaginous fish Reptiles Mammals Amphibians Flowering plants 10° 107 known for a long time because they are what are used to identify species and individuals! Restriction fragment length polymorphisms are produced from unique sections of DNA (the polymorphic segments) when the polymer is cut up (restriction digests by endonuclease enzymes), and they produce what is referred to as the "DNA fingerprint". This is what is used to identify specific species, sub-species and clades, all the way down to individuals. This should have been a big clue: if you're looking for what makes a species different from any other species, the sections of DNA that are used to identify a particular species or individual would be a good place to start! These unique sections of DNA are the non-coding segments. Calling these sections of the genome "junk DNA’ is like calling the engine of a car the "spare tyre”. How important are the non-coding sections of the DNA? One indication should be their prevalence in the genome. In humans, 95-98 per cent of the genome is non-coding! This is similar for some other species, yet there is a correlation between increasing organismal complexity and the amount of non-coding DNA. For example, bacteria such as Escherichia coli have exceedingly little intergenic DNA. Their genomes are architecturally simplistic, being simple circular strands that are unlikely to adopt complex configurations, yet they still have approximately 4,290 genes. That's one- fifth the amount in humans, who contain approximately 21,000 genes, and yet these E. coli are microscopic bacteria! In fact, Caenorhabditis elegans, a small worm, contains more genes than humans do. However, in this context, what humans do have more of is non-protein- coding DNA, as can be seen by the correlation of genome size with non-coding DNA (a great deal of the large genome sizes of plants is due to polyploidy—multiple sets of the same chromosomes which are sufficient to produce speciation without a single change to a protein-coding gene). The non-coding segments have three primary functions identified thus far... ¢ About half of the non-coding genomic regions are comprised of mobile genetic elements which modulate gene expression and can remodel the chromosomes. ¢ The other half is comprised of variable-number tandemly repeating sequences, known technically as satellite DNA. Through specific conformational arrangements, they interface with the morphic field. NEXUS ¢ 49 Genome sizes of various organisms according to number of nucleotide base pairs FEBRUARY - MARCH 2012 www.nexusmagazine.com