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DNA / RNA

The vast majority of human DNA lies outside of the genes within the cells. Of this, recent work has discovered that 85% of these stretches of DNA appear to make RNA - which, for the most part, have yet-to-be-determined functions.

A study published in the online journal PLOS Genetics on June 20, 2013, from the McManus Lab. at the University of California SF points out that :

Today, scientists estimate that only 1.5 percent of the genome consists of genes."

The lab investigates the remaining 98.5% - which (referencing similarly-scaled problems in cosmologyplugin-autotooltip__plain plugin-autotooltip_bigDark Matter

"The nature of the dominant component of galaxies and clusters remains unknown."

Source : Measuring the dark matter equation of state (Mon. Not. R. Astron. Soc. 415, L74โ€“L77)"

In the 1930s, astronomical observations of galaxy rotations showed that the outer regions were rotating (about the galaxy's 'centre') at the same speed, or faster, than the central regions. Subsequent calculations referring to the galaxy's mass, and thus its internal gravitational attractions, showed that iโ€ฆ
) they call the 'Dark Matter' of the human genome.

Much of the human genome is composed of intergenic sequence, the regions between genes. Intergenic sequence was once thought to be transcriptionally silent 'junk DNA', but it has recently become apparent that intergenic regions can be transcribed. However, the scope, nature, and identity of this intergenic transcription remain unknown. Here, by analyzing a large set of RNA-seq data, we found that >85% of the genome is transcribed, allowing us to generate a comprehensive catalog of an important class of intergenic transcripts: long intergenic noncoding RNAs (lincRNAs). We found that the genome encodes far more lincRNAs than previously known."
We believe that the regulatory noncoding RNAs that have been discovered are just the 'tip of the iceberg' in a set of important biology that we are far from understanding."

Further reading : Junk DNA: A Journey through the Dark Matter of the Genome by Professor Nessa Carey, Columbia University Press, 2015.

Junk DNA can play vital and unanticipated roles in the control of gene expression, from fine-tuning individual genes to switching off entire chromosomes. These functions have forced scientists to revisit the very meaning of the word "gene" and have engendered a spirited scientific battle over whether or not this genomic "nonsense" is the source of human biological complexity."

UNICORNs

A 2023 study, which examined the DNA of the mammal group, identified nearly half a million 'regulatory elements' (outside the genes) which they call UNannotated Intergenic COnstrained RegioNs (UNICORNs)

The research team suggest that the UNICORN regions very probably have functions in demarcating genetic elements that are important in tissue types, or at development time points.

"[they] almost certainly affect gene regulation in ways that are not yet understood." Ref. Scientific American, Apr. 2023.


Also see: Genome sizeplugin-autotooltip__plain plugin-autotooltip_bigGenome size

The size of the genome (which can be said to be the amount of DNA in an organism's genes) varies enormously from one species to another. The smallest size, for viruses, varies from 2 thousand base-pairs to over a million.

Humans have about 3 billion (forming around 19,000 genes) - but some plants have more than 10 times as much. The lack of correlation between the apparent complexity of an organism and its genome size is called the

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