How Much Of The Human Genome Is Junk?

Scientists are still sorting out how much of the genome is functional and how much is so-called "junk DNA."
(Photo : Getty Images/William Thomas Cain)

The roughly 3 billion letters in the human genome were sequenced in 2001.

Scientists are still sorting out how much of the genome is functional and how much is so-called "junk DNA" or serves no useful purpose.

In a new study, researchers at Cold Spring Harbor Laboratory (CSHL) have developed a novel computer program to identify which letters in the human genome have a function, reports Science Daily.

For the study, the researchers used the program called fitCons to compare changes in DNA in related species and also among numerous individuals in a single species.

The researchers found that roughly 7 percent of the letters in the human genome serve an important function.

"In model organisms, like yeast or flies, scientists often generate mutations to determine which letters in a DNA sequence are needed for a particular gene to function," said Adam Siepel, a professor of computational biology at CSHL.

"We can't do that with humans. But when you think about it, nature has been doing a similar experiment on a very large scale as species evolve. Mutations occur across the genome at random, but important letters are retained by natural selection, while the rest are free to change with no adverse consequence to the organism," Siepel added.

The National Human Genome Research Institute started the public research consortium ENCODE to create an encyclopedia of DNA elements.

"Other groups have sequenced large numbers of humans and nonhuman primates. For the first time, these big data sets give us both a broad and exceptionally detailed picture of both biochemical activity along the genome and how DNA sequences have changed over time," according to Siepel.

"ENCODE provided us with information about where along the full genome DNA is read and how it is modified with biochemical tags," said Brad Gulko, a Ph.D. student in Computer Science at Cornell University and the lead author on the study.

"Our analysis helps to pinpoint which letters in these sequences are likely to be functional, because they are both biochemically active and have been preserved by evolution." Siepel said. "This provides a powerful resource as scientists work to understand the genetic basis of disease."

The research was published in the journal Nature Genetics.


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