Saturday, 24 March 2012

Jumping Genes: How They Drove Primate Evolution


By Daniel Rouse

Original Article: Oliver, K & Greene, W 2012, 'Jumping Genes: How They Drove Primate Evolution', Australasian Science, vol. 33, no. 1, pp18-21.

Less than 2% of the DNA in the human genome is used for coding proteins. The remaining 98% is known as non-coding DNA. Of this, approximately half are jumping genes – also known as transposable elements. They move from one part of the genome to another in a process called transposition.
American geneticist Dr. Barbara McClintock first identified jumping genes in the 1950s when researching the genome of Indian corn. At first her discoveries were met with severe skepticism, to the point of her not publishing findings for many years. In more recent history, the scientific community has realised that she was right all along – and she won the Nobel Prize in 1983 for her work in the field.
McClintock’s identification of jumping genes came about when researching the mutated pigmentation of Indian corn, which defied Mendel’s basic principles of inheritance.
 Figure 1: Indian corn kernel exhibiting jumping gene activity (Armstrong 2000)
Despite the name, jumping genes do not detach from the cell’s DNA – the strand is ‘bent’ by enzymes and other proteins so that the origin and destination sites of the jumping genes are brought together for transposition to occur. 
Nowadays these genes are known to be found most species of both prokaryotes and eukaryotes, and make up large percentages of all DNA. 
Jumping genes are an excellent way to throw up new mutations. And while their existence has been known for some time in the scientific community, only now have scientists at Murdoch University pieced together the relationship between them and major advances in primate and human evolution.  
  
The major downside to the activity of jumping genes is that, depending on where they transpose to in the genome, they can cause genetic disorders including certain forms of hemophilia and cancer.
However, most jumping genes are inactive. This is because the structure of the genome inhibits most jumping gene activity, resulting in a balance between beneficial and detrimental mutations.
Jumping genes therefore can stimulate the birth of lineages within a species that possess significant advantages within a population. 

Figure 2: Representation of transposon inserted into inside of gene (SoftPedia 2012)

The source article theorises that major developments in primate evolution can be attributed to episodic spurts in transposition. Over the course of the evolutionary history of primates, jumping genes have:
  • Caused the activation of the enzyme amylase, which has resulted in humans being able to digest starch;
  • 'Pasted in’ next to the antimicrobial gene CAMP meaning that it is now activated by Vitamin D when a person is exposed to sunlight;
  • Created the GLUD2 gene, which speeds up learning and memory in humans and our primate cousins; and
  • Removed the dangerous CMAH gene from humans about 2 million years ago, which caused sialic acid molecules to form on human cells.
In conclusion, it is well known that jumping genes cause changes to the DNA sequence in organisms, and consequently in species as organisms father lineages which dominate the gene pool. Jumping genes are present in large numbers, in most species’ genomes. It is also known that jumping genes can activate both advantageous and nonadvantageous mutations.

To see a recent video explanation from Dr McClintock’s DNA Learning Centre (Cold Stream Harbour Laboratory, New York), click here:
http://www.youtube.com/watch?v=9MPiRx3SPMM

For a more humorous look at jumping genes, click here:
http://www.youtube.com/watch?v=27n2Y5UJNmo

Bibliography

Anitei, S 2006, Jumping Genes Could Cure Genetic Maladies, 26 September, SoftPedia, viewed 19 March 2012, .

Armstrong, W 2000, Transposons (Jumping Genes), Wayne’s Word: An Online Textbook of Natural History, viewed 19 March 2012, .

Oliver, K & Greene, W 2012, ‘Jumping Genes: How They Drove Primate Evolution’, Australasian Science, vol. 33, no. 1, pp18-21.

Pray, L 2008, ‘Transposons: The Jumping Genes’, Nature Education, vol. 1, no. 1, viewed 19 March 2012, .

Rampling, J 2011, Jumping Genes Helped Evolution, Science Alert, viewed 19 March 2012, .

Reece, J, Meyers, N, Urry, L, Cain, M, Wasserman, S, Minosrky, P, Jackson R & Cooke, B 2012, Campbell Biology, 9th edn, Pearson, Australia.



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