98.5% of DNA is useless?

Question

I just finished watching a DVD called "Cracking the Code of Life", and in one part, a scientist told the interviewer that only 1.5% of human DNA is genes, and the other 98.5% is useless DNA that have survived since the beginning of life and are just hitchhiking on our bodies. Is that true?

Answer 1

There are many aspects to your question, and I will try to go in order.

Useless DNA: Yes, a lot of DNA in our body is non-coding, which means that it does not code for a particular protein or RNA. This was previously called "junk DNA". However, scientists have been working very hard to answer your very question, and they saw that the non-coding region had some very interesting uses. It contained sequences that seemed to regulate the coding portions. These regions are called regulatory regions or promoters. One gene can have more than one promoter region. Scientists have also proposed a very interesting hypothesis about the large amount of non-coding DNA in our genome. They suggest that the non-coding DNA could act as a buffer and absorb the harmful mutations. DNA is prone to mutations. If the mutations occur in the coding region, the organism might not be able to survive. By having large gene deserts, the genome is increasing the probability that non-coding regions will be hit more than the important regions.

Scientists have also proposed another very interesting hypothesis. They say that these non-coding regions could play a very important role evolutionarily. Some times, regions of DNA duplicate, and one of them gets mutated, which helps make it a functional gene!

Despite many studies, there is no concrete answer yet to the function of all the non-coding regions in our genome, but as scientists spend more time analyzing the information made available, we will get better answers to your question

Answer 2

I'm a college student, and I just got out of a Genetics class this semester, so that can kind of back up my answer a bit. To answer your question, I think the scientist was talking about the actual "coding" genes that make proteins, which is actually a minority in the whole genome. 20,000-50,000 genes, out of billions and billions of base pairs. You know, the base pairs are A-adinine, C-cytosine, G-guanine, and T-thymine. The "junk" DNA includes the stuff that either doesn't seem to do anything, or we don't yet understand. A huge portion of the junk has now been called promoters, which are in front of every gene, and it tells how much, or often, that gene should be transcribed and translated into a protein. They're pretty important, since some proteins are absolutely necessary, (like hemoglobin in blood), and others are only needed rarely, and promoters were once labeled junk. So were telomeres, which is actually REAL junk at the end of a chromosome. Usually GGAAA repeated over and over. But they are put there as the embryo forms because chromosomes actually shorten a tiny bit every time a cell divides. Shortening telomeres after many years getting into "coding" DNA regions actually is believed to cause aging. Wow, I've wrote more than I thought... I hope I answered the question. A small part actually codes for protein, maybe 1.5%, I've heard as much as 5% or 7%. Someone else mentioned meiosis, and crossing over. Another reason there's so much junk in between genes is so crossing over between chromosomes doesn't cut into genes. It's all about genetic diversity. The rest is promoters, regulators, and maybe old stuff leftover too.

Answer 3

Not really "useless", but not as functional in encoding proteins. Genes are DNA sequences that instruct the cell on how to make proteins from amino acids, which interact with other proteins to do basically everything in the cell. While only 1.5% of human DNA encodes genes, the other parts of DNA (enhancers, promoters etc...) commonly contain regulatory regions that tell the cell where the genes are and to start making protein from them.

One way to look at the importance of a sequence is to see what happens to cellular function if you mutate it. If you mutate a portion of a gene encoding protein, you're likely to get a non-functional protein. If you mutate a portion of DNA outside of this, it MAY have no apparent function at all.

DNA can also serve structural roles in helping other DNA to be in the right portion of the nucleus so that it can be recognized. While there is probably a lot of DNA that doesn't have a specific identifiable function, I believe that there are many complex functions in the cell that are not yet understood but may be critical.

Answer 4

I don't know if that number is correct but yes it is true, there is "junk" DNA.

Scientists don't know exactly why it is there, some theories include that it is simply old DNA thats not used, other theories think it may be there to have a "safe" spot for mutations to happen to your DNA where it is not likely to affect any genes. Also it is known that a lot of non-gene coding DNA is used for regulation of gene expression and in the initiation and termination of DNA transcription.

When your DNA is being transcribed so the genes coded can be used sometimes this "junk" DNA is in the gene it self. These are called introns, and the region coding for a gene is called an exon. The introns are removed from the transcribed sequence before it is translated into something the body can use.

Answer 5

Partly it is correct. That is only about 1-2 % of the entire genome codes for Genes. However, rest is "Junk" - Not true.

Is there any "junk"

The first systematic analysis of a significant portion of the human genome was published in June, 2007 (see below). The analysis attempted to determine the function of entire regions of DNA. The results showed that, although only a small amount of the genome codes for protein, most of the rest is still transcribed into RNA, which functions in ways not described before. As more is learned about the structure of the human genome, it is apparent that most (if not all) of the non-coding regions of DNA are required for the proper functioning of the DNA.

Answer 6

The noncoding potion has function of a different type. There are promoters and other regulating sequences. The telomeres have a function in both cell aging and cancer prevention. As the cell divides the telomere is shortened meanwhile DNA editing may allow errors to accumulate risking oncogenesis. Once the telomere is too short, the cell can't divide and becomes senescent or dies. There are palindromic repeats that cause loop & stems (like those in tRNA) in the y chromosome that aids in editing & repairing errors in sequence.

http://www.nature.com/nature/journal/v423/n6942/full/423810a.html
http://en.wikipedia.org/wiki/SRY

MARs is the sequence where scaffolding protein attaches.
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TCY-47S6N3H-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=170798bae055a4b5883206a4b3e23364

There are pseudogenes where function seems lost but they are occasionally conserved across species so must be under some selective pressure to be maintained. They are called pseudo because they have sequence very close to a known gene but do not have an intact open reading frame. framshttp://compbiol.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pcbi.0020046

There are regions of DNA that are transcribed but not translated producing noncoding RNA - ncRNA. This includes tRNA, siRNA, microRNA, & piRNA.
Many of these are involved in silencing invading genome invaders.
http://www.rnaiweb.com/RNAi/What_is_RNAi/
We are only beginning to understand how the cellular processes function so definitive pronouncements like the old paradigm of 'one gene one protein' have been up dated by new information.

Answer 7

It is true, 98.5% is considered "Junk DNA"(non-coding) Only 2.5% actually codes for proteins. Although 98.5% is considered "Junk," it is not useless.

1. Non-coding DNA serves as an on/off switch. most genes that are needed are turned off, the one's needed are turned on.

2.Gene expression- Determines how much of a protein is made.

3. DNA fingerprinting- looks at the space between the genes.

Answer 8

Untrue! That video must have been a few years old. While we once thought 98.5% of our DNA was "useless" because it didn't code for any usefull products, recent research has shown that that 98.5% plays an importent part in the regulation of gene expression and other roles.

Answer 9

It is not exactly what you call "useless." 98.5% of DNA is the same for all of us. This percentage is what make us similar in terms of 2 legs, hands, eyes etc. It is the 1.5% that determine our more distinguishable features i.e, the characters we receive from our parents. This 1.5% is more useful because, as i said, they distinguish each individual from the other. Thus they can be used in Forensic analysis to find the culprit for a crime. this 1.5% is DIFFERENT FOR EVERY INDIVIDUAL.

And yes the 98.5% DNA has been there in humans from the beginning of life.

Answer 10

1.5% of your DNA codes for genes. The rest has been called "junk" in the past, but scientists are discovering that this "junk" DNA actually has a purpose. One important purpose is to regulate gene expression. This "junk" DNA also includes telomeres and centromeres, which are important in DNA replication and cell division. Also included in this "junk" DNA is actual junk, but it is not 98.5% of the genome.