Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: thedoc on 27/09/2016 09:53:02
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Luke Pullar asked the Naked Scientists:
Hi Chris et al
When manipulating an animal's genes (such as how this article suggests), how is this done? Do the changes replicate throughout the body, or only through a localised area? And will such a change pass on through reproduction if the genes have been changed through such an external agent?
Thanks guys and gals. It's great listening to your shows, and I'm slowly working through the back-catalogue of your podcasts (http://www.thenakedscientists.com/HTML/podcasts/).
Luke Pullar
What do you think?
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When manipulating an animal's genes, how is this done?
In prehistory, it was done by selective breeding - breeding animals and plants that had desirable genetic characteristics that occurred in nature.
In the past century it was accelerated by some hit-and miss methods like subjecting plant and animal cells to nuclear radiation or mutagenic chemicals, and just seeing what happened.
In the past couple of decades it has become a bit more targeted with the ability to manipulate DNA, for example by putting a desired gene into a retrovirus and letting the virus infect some cells; the virus then inserts this gene some random place in the DNA.
In the past 5 years, some very targeted methods have become available - one causing a lot of excitement among geneticists is CRISPR/CAS9 (https://en.wikipedia.org/wiki/CRISPR), which allows researchers to locate a specific DNA sequence (with >90% accuracy), chop it out and replace it with a different bit of DNA.
See: https://en.wikipedia.org/wiki/Genetic_engineering
Do the changes replicate throughout the body, or only through a localised area?
The genetic change will only occur in the cells receiving the genetic change. If it is carried by a virus, the virus is disabled so it can't spread through the patient's body (and perhaps be caught by other people, creating an epidemic of genetic change).
Some genetic treatments proposed for cystic fibrosis have the patient inhaling viruses which make genetic changes to the cells lining the lungs.
Some treatments proposed for genetic blindness propose injecting the required genes directly into the eye.
And will such a change pass on through reproduction if the genes have been changed through such an external agent?
If genes are modified in reproductive cells (plant seeds, eggs, sperm, ovaries, testes or the fertilized eggs of "test-tube babies"), then the modified genes will be carried by any organism growing from these cells. And by perhaps 50% of their children.
At present there is a ban on human reproductive manipulation, even for therapeutic reasons.
So you can test a treatment that cures a patient, but you are not permitted to test a cure that would cure their children.
There are some exceptions:
- some countries permit "3-parent" babies, which don't add any new genes apart from those in the parents.
- Some countries enforce no rules at all.)
There are no similar strict controls on research into genetically modified plants or animals - and some environmental groups are very worried about it.
How much of an impact can manipulating an animals genes have?
Geneticists looking for resistance to various diseases often go hunting for the wild ancestor of a modern domesticated species.
And often, if you put the two together, a non-specialist would not recognize that they were related.
- The ancestor of the (almost-disabled) pug dog is the powerful wolf
- The ancestor of the delicious, juicy pineapple has a small, woody fruit
- The ancestor of most of the grains we eat (rice, wheat, etc) is grass
- And these dramatic changes were achieved by breeding, without any artificial genetic manipulation
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A story from this week's Naked Scientists podcast describes a way to get genetic information into cells of a living creature by injection into the bloodstream.
The genetic material is attached to a peptide which is taken up by the cell (and, reading between the lines, transported into the cell nucleus by cellular mechanisms).
Getting genetic material into the cell has always been a challenge - the cell has several mechanisms to detect and attack viruses, and most organic materials are digested before they can deliver their genetic message into the cell nucleus.
See: http://www.thenakedscientists.com/HTML/interviews/interview/1002031/