Oncology & Cancer

Scientists find surprising impact of junk DNA and RNA in cancer

"Human satellite II," an exceptionally high-copy but unexplored sequence of the human genome thought of as "junk DNA," has a surprising ability to impact master regulators of our genome, and it goes awry in 50 percent of ...

Arthritis & Rheumatism

Juvenile arthritis: why genetic risk is not in the genes

Scientists have been finding that genetic risk for many diseases lies primarily in noncoding parts of the genome, which used to be called "junk DNA," and not in the genes themselves. But that finding naturally begs more questions ...

Genetics

MicroRNA, the puppet master of the genome

We all know how irritating it is to have an inbox flooded with junk mail. Fortunately email providers these days contain filters to keep the junk mail at bay. As a result the junk mail folder tends to pile up with never-to-be-read ...

Diabetes

Key protein accelerates diabetes in two ways

The same protein tells beta cells in the pancreas to stop making insulin and then to self-destruct as diabetes worsens, according to a University of Alabama at Birmingham (UAB) study published online today in the journal ...

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Junk DNA

In evolutionary biology and molecular biology, junk DNA is a provisional label for the portions of the DNA sequence of a chromosome or a genome for which no function has been identified. The term was introduced in 1972 by Susumu Ohno, but is as of 2008 somewhat outdated, being used mainly in popular science and in a colloquial way in scientific publications. For some sequences once classified as junk DNA, functions have been found, and others are subject to ongoing research. About 95% of the human genome has once been designated as "junk", including most sequences within introns and most intergenic DNA. While much of this sequence may be an evolutionary artifact that serves no present-day purpose, some junk DNA may function in ways that are not currently understood. Moreover, the conservation of some junk DNA over many millions of years of evolution may imply an essential function. Some consider the "junk" label as something of a misnomer, but others consider it appropriate as junk is stored away for possible new uses, rather than thrown out; others prefer the term "noncoding DNA" (although junk DNA often includes transposons that encode proteins with no clear value to their host genome). About 80% of the bases in the human genome may be transcribed, but transcription does not necessarily imply function.

Broadly, the science of functional genomics has developed widely accepted techniques to characterize protein-coding genes, RNA genes, and regulatory regions. In the genomes of most plants and animals, however, these together constitute only a small percentage of genomic DNA (less than 2% in the case of humans). The function, if any, of the remainder remains under investigation. Most of it can be identified as repetitive elements that have no known biological function for their host (although they are useful to geneticists for analyzing lineage and phylogeny). Still, a large amount of sequence in these genomes falls under no existing classification other than "junk". For example, recent experiments removed 1% of the mouse genome and were unable to detect any effect on the phenotype. This result suggests that the DNA is nonfunctional. However, it remains a possibility that there is some function that the experiments performed on the mice were merely insufficient to detect. This can also be evidence for reconstructing ancestral lineages.

While overall genome size, and by extension the amount of junk DNA, are correlated to organism complexity, there are many exceptions. For example, the genome of the unicellular Amoeba dubia has been reported to contain more than 200 times the amount of DNA in humans".

The pufferfish Takifugu rubripes genome is only about one tenth the size of the human genome, yet seems to have a comparable number of genes. Most of the difference appears to lie in what is now known only as junk DNA. This puzzle is known as the C-value enigma or, more conventionally, the C-value paradox.

This text uses material from Wikipedia, licensed under CC BY-SA