Genes that come from No Where!
Genetics has come a long way since the 1950’s. Although there has been progress made in unravelling the mysteries of our molecular heritage, we are constantly stumped by newer facts about our genetic code. And the one that leads the way is the mystery about Junk DNA.
Genes, our molecular hereditary information, although bulky and cumbersome have a methodical way of working. Genes are transcribed into RNA which in turn are coded into protein, and these proteins finally get involved in the molecular build-up of our existence, thus making the genes where they come from, the foundation of it all.
But not all of the gene or genetic material is really coded into protein. There is a major portion which is left out of this entire process and is not capable of coding for protein; this is called ‘junk DNA’. Interesting facts about ‘junk DNA’ have baffled the world of science, like the ‘junk DNA’ constitutes almost 95% of the human genome!
For years the scientific world was intrigued by these ''left overs'' in our genome. There was definitely a reason why it was there but no one could find out why. Junk DNA was one part of genetics, that despite all the progress made in the field, became every molecular geneticist’s nightmare.
Along with various theories that attempt to reason the functionality of Junk DNA, a concept that is fast grabbing the attention of geneticist’s is that junk DNA actually gives rise to new genes.
‘De novo’ (Latin for anew, afresh) origin of genes was an absurd idea and was practically discarded by the scientific community in the late 1970’s (Jacob F. 1977). But recent discoveries and wider understanding of the genetic code shows that organisms at every level of evolution have genes that are ‘De novo’ in origin. Studies on Drosophila (house-hold fruit fly often seen hovering around bananas) in 2006 (Levine et al) actually opened the door to the origin of genes from non-coding, ‘junk DNA’. By 2008, it was estimated that around 11.9% of new genes in the Drosophila had a de novo origin (Zhou et al)! These studies have not been restricted to fruit flies. Soon scientists discovered genes of de novo origin in Saccharomyces cerevisiae (yeast), mouse, rice and Humans. In fact a study in 2010 by Li et al, describes a gene associated with human brain function, originated from Junk DNA.
In an interesting paper recently published in PLoS (Public Library of Science) Genetics journal, Dr Wu Dong (2011) along with his colleagues report a total of 60 supposedly human genes that had ‘de novo’ origin which basically means, 60 genes which seem to have had no record of existence before, were now traceable to certain Junk DNA fragments. This is surprising since papers printed just a year prior claimed a maximum of 18 human genes could be de novo in origin.
The study was taken a step further and these reported genes were compared to our closest evolutionary relative, the Chimpanzee. Since the study could not find these genes in the Chimpanzee genome, it was speculated that these de novo genes may be the key to recognizing the fundamental differences between the two species and may also hold vital clues in the mystery called, the evolution of Man.
What is more fascinating is that these ‘new’ genes seem fairly simple in comparison to existent genes, (i.e they are short and consist of only one exon, or the sense region), so according to scientists, their de novo origin seems highly plausible. Although their function is not exactly known, these set of de novo genes have been recorded to express the most in the testes (which will allow them to be passed on to the next generation) and brain tissue (plausible they have an effect on the way we think).
For now, we will leave you these thoughts; do we really know if there is anything called ‘junk DNA’? How many genes might be hidden in our ‘junk DNA’? if not, why is it there?
References for the interested reader:
References for the interested reader:
- Dong et al 2011- De Novo Origin of Human Protein-Coding Genes
- Gregory et al 1999- The Modulation of DNA Content: Proximate Causes and Ultimate Consequences
- Jacob F. 1977- Evolution and Tinkering.
- Levine et al 2006 – Novel genes derived from non coding DNA in Drosophila melanogaster are frequently X-linked and exhibit testis based expression.
- Li et al 2010 - A Human-Specific De Novo Protein-Coding Gene Associated with Human Brain Functions
- Zhou et al 2008 – On the origins of new genes in Drosophila
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