What was the need of junk DNA from evolutionary point of view?

Question

Wouldn't it have saved us a lot of space and energy required in its replication if we simply didn't have junk DNA? Why is it there?

Answer 1

Thats an excellent question, and one that nobody knows the answer to...we dont even know for sure if it all HAS a purpose, but there are some theories.
One is that there are hidden regulatory sequences that we are just ignorant of
One is the this is important somehow for the physical structure of the DNA-the 3-dimensional packing of it
Of course we know from sequencing the a lot of it seems to be inactivated genes....

Answer 2

Not everything in life has a function ... this is one reason why evolution provides a better theory than intelligent design ... ID cannot explain junk DNA *at all*.

It may just be that saving the extra energy involved in replicating useless DNA is just not worth the extra energy that would be required to get rid of it. I don't know about you, but I have a lot of boxes in my garage full of useless papers that have been following me around from move to move for years ... the energy required to go through it and salvage the few scraps I still care about far exceeds the energy required to just throw the box on the moving truck each time I move.

That said:
1. Some junk DNA may have a function we have not discovered yet (such as a buffering between codons).
2. Some may once have had a function, but no longer does (i.e. coded for some structure or protein that is no longer used).
3. Some may have a function that may be re-activated.
4. Some may be dead ends in evolution, a mutation that was neither useful nor harmful, but is being carried along for the ride.

In short, junk DNA may just be a side-effect of the process of evolution ... rather than a central feature with a function.

It may just be that mechanisms that clean up junk from the genome are more dangerous (because they are more likely to delete something essential) than the main mechanism for adding new material (namely gene duplication events, which are more likely to be neutral).

It also may be a natural consequence of the 2nd Law of Thermodynamics ... junk DNA represents the accumulation of entropy.

Answer 3

None, perhaps. I like to theorize that it wasn't "needed" from an evolutionary point of view, but rather created from evolution. Take for example, the appendix. It doesn't have much of a use, but its still there because apparently cavemen used it to eat raw meat. Well in the same sense, junk DNA could be DNA for things that aren't needed any more. The DNA, however, is still present despite the absence of the body part because DNA is always passed on and can't just disappear between generations.

Answer 4

Recently, non-coding DNA has been shown to contain regulatory regions which control the expression of genes and maintenance of telomeres so not all junk DNA is junk. These snRNAs can be important in adapting to different environments, particularly when under stress.

Also it is good to have space between genes and even within them. One thought for this is that it allows for the accumulation of mutations without being detrimental to the organism. Mutations happen, but given that 97%(?) of the genome is considered junk, the probability of them affecting a coding region is low.

This also leads into another function. It gives the genome a place to experiment. Over time genes can duplicate, diverge in function, and perhaps become pseudo-genes in the confines of the junk region. It serves as a place for transposons to land without disrupting genes.

As for saving space, non-coding DNA can serve structural purposes. For instance DNA is wrapped around histones so not all of it is easily accessible for replication. The space between genes may put the genes in the proper phase.

Answer 5

In molecular biology, "junk" DNA is a collective label for the portions of the DNA sequence of a chromosome or a genome for which no function has yet been identified. About 97% of the human genome has 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 may function in ways that are not currently understood. In fact, recent studies have suggested functions for certain portions of what has been called junk DNA. 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 apposite 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).

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".

Overall genome size, and by extension the amount of junk DNA, appears to have little relationship to organism complexity: the genome of the unicellular Amoeba dubia has been reported to contain more than 200 times the amount of DNA in humans"

Answer 6

Junk DNA is thought to have arisen as a type of barrier between codable genes. in this sense they do serve a purpose. Other types of junk DNA called "pseudo genes" are thought to have arisen when a type of genetic virus "implanted" them in our code. They are no longer active or even harmful, but they are still there in our gene sequence. Even these genes help in the spacing of codable genes to allow space during replication and translation.

Answer 7

I think junk DNA is just like vestigial sequences, they were once functional, but due to repeated mutations, they have lost their functionality but we have simply not gotten rid of them.
Maybe they contribute to genome plasticity and can become functional again, through mutations.