Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS
DNA
The Secret of Life Playing God Human Race Curing Cancer Pandora's Box Timeline 3D DNA Explorer
Episode 5 : Pandora's BoxEpisode 5 : Pandora's Box

Special Report
Beyond DNA: Genetics of the Future, by Magdalena Eriksson: Page 2 of 2
Back to page 1
Return to episode intro

Comparisons of mammalian genomes have shown that certain tracts of the "junk" show a high degree of similarity among various species. This means that these conserved tracts are actually remnants of primordial DNA that have remained the same for 300 million years as mammals have evolved in different directions, which also suggests that they provide indispensable functions. The number of such non-coding regions of DNA has been estimated to exceed the number of protein-coding sequences. The search to explain the role of conserved non-coding DNA will likely occupy researchers for years to come.

Test tubes
When resting, DNA is coiled around protein complexes like thread on spools, making two turns around each spool of proteins.

Some stretches of DNA are necessary for correct packing of the enormously long molecules into compact, well-ordered chromosomes. When resting, DNA is coiled around protein complexes like thread on spools, making two turns around each spool of proteins. Little chemical markers lock the DNA to these spools. If these markers disappear, the genes they normally hold in place are taken out of storage and become available to enzymes that can read their code and use them for protein production. This lost marker function can be passed from one generation to the next, thus showing how our genome can carry inheritable traits that don't require a change in the DNA sequence. This phenomenon is called epigenetics.

Epigenetics suggests how evolution may be sped up. Minor or temporary changes in lifestyle or environment that occur before or during reproduction can cause visible changes in the next generation. Epigenetic changes may serve to allow us to respond swiftly to altered environmental conditions. Darwinian evolution, which involves long-term changes in the genome's DNA sequence, operates on a much slower timescale.

Another recently discovered genetic regulation involves non-coding stretches of the genome. These stretches turn into powerful tools when translated to RNA. Nature has invented its own remarkable strategy of silencing genes so that their information is hidden from enzymes, a stratagem called RNA interference (RNAi). Short pieces of double-stranded RNA dock at matching sequences of messenger RNA where they attract a protein complex, which efficiently breaks up the coding sequence and prevents protein from being created. This sort of control over when to turn on and off different genes is the basis of development; the right type of tissue has to grow at the right time.

Scientists have learned how to use RNAi in the laboratory, and the technique has become a popular research tool. It is possible to insert tailor-made pieces of RNA into cells. When these bits of RNA find their target in the genome, that part will be shut down. Researchers can then establish what effects the RNAi and the shut-down gene have by examining changes in the cells. Scientists are already exploring the use of this RNAi technique for medical purposes, including the study of various cancers and viruses, as well as HIV and the malaria parasite. It may also be used in combination with gene therapy.

Our understanding of how DNA runs the human anatomy is still fragmented -- we understand certain processes and principles in great detail, whereas others are still unclear. Some remain unknown. It seems the more we learn, the more we realize how much is left to explore.

back
Return to Episode Intro
DNA sequence
DNA lab
Microscopic material

Tools
Glossary
E-Mail this page

For Teachers DNA Resources Feedback Support PBSSupport PBS Credits