Gene. (Introns are removed, or ‘spliced’, before the assembly of the protein.)
(Source: Wikimedia Commons, Courtesy of National Human Genome Research Insititute)
The human genome is estimated to contain about 23 000 genes. Where do these genes come from? Well, from your parents. And their parents. And so on. But, surely, if we go back far enough, there haven’t been 23 000 genes all along? However life originated, the first DNA carrying organisms probably had significantly fewer genes. So, where did all these new genes come from? How are genes born?
Well, there are two main ways:
- Re-organization of existing genes. For example, sometimes, genes get duplicated. One of the two copies can then get co-opted for a new function. Ta-dah. New gene.
- All new. In other words, not based on previously present genes. This is what the new study investigates.
The basic idea is this:
DNA
(Source: Wikimedia Commons, author: mstroeck)
A lot of DNA does not specifically code for proteins. However, sometimes it might get translated, resulting in fairly insignificant chains of amino acids. But, so the authors argue, these insignificant chains might provide “raw material for natural selection”. At this point, the non-genic sequences become proto-genes. If whatever they code for provides a benefit for the organism, these proto-genes could be retained and might, over time, become real genes.
To check their idea, the research team turned to the ever popular baker’s yeast (Saccharomyces cerevisiae). The authors found three things that support their model of de novo gene birth.
- The open reading frames (or ORF’s, stretches of DNA that don’t code for a ‘stop’ signal) form a continuum, from non-genic to gene.
- Many of the non-genic ORF’s get translated occasionally.
- The products of these non-genic ORF translations appear to show some adaptive potential, as the regulation of their translation changed with the environmental conditions.
In short: non-genic ORF gets translated -> proto-gene. If product of proto-gene beneficial -> Proto-gene gradually becomes ‘real’ gene.
Or, the birds and the bees, the genetic version.
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Carvunis, A.-R., Rolland, T., Wapinski, I., Calderwood, M.A., Yildirim, M.A., Simonis, N., Charloteaux, B., Hidalgo, C.A., Barbette, J., Santhanam, B., Brar, G.A., Weissman, J.S., Regev, A., Thierry-Mieg, N., Cusick, M.E., & Vidal, M. (2012). Proto-genes and de novo gene birth. Nature, 487, 370-374 DOI: 10.1038/nature11184
