|MadSci Network: Genetics|
Hi Young, Before I answer your question, I recommend that you take a look at the madsci website http://www.madsci.org/join/, where you will find that the qualification for participating in MadSci is "Knowledge of a particular area of science and a willingness to communicate your expertise with others." If you look at the list of participating scientists for any area at MadSci ( http://www.madsci.org/MAD.scilist.html ) you will see a breadth of background from undergraduates through full faculty members and everything in between. We aren't necessarily world renowned leaders in our field; we are simply individuals with a better than average background in our favorite fields, willing to do our best at answering scientific questions submitted from the larger community. I happen to hold a Ph.D in genetics from Stanford University, but I am not actively involved in cloning research. Now to your question: how did cloning help us in the past? First I want to discuss the meanings of "cloning". More than two decades ago it became possible to splice together bits of DNA and replicate the spliced product. This process has become known as cloning, based on the fact that once a specific bit of DNA is spliced into a vector it may be replicated as many times as you want. This type of cloning revolutionized the world of molecular biology, allowing us to easily perform tasks as diverse as production of enzymes from cloned genes, sequencing of cloned DNA, and even mapping the human genome using large libraries of clones which each contain a small portion of the overall genome. However, I suspect that you didn't actually mean cloning in that sense. The meaning of cloning which is more prominent in the media today is the duplication of an organism using the same genetic blueprint. While it certainly made a splash when "Dolly" the sheep was cloned, natural clones have existed since the dawn of time: in many organisms (bacteria and many fungi come to mind) there is no sex, and all offspring are genetically identical to their parents. In higher organisms (plants and animals) it is more common to reproduce sexually, although there are some interesting exceptions to the rule. For example, in reptiles sex is not determined by an X and Y chromosome, but by the temperature at which the eggs incubate. Higher temperatures generally produce females. In desert regions many species of lizard have been identified in which all eggs develop as females. For a sexually reproducing organism this would have rather disastrous results within one generation, but these lizards are capable of reproducing clonally. All daughters are clones of their mother. While this is certainly an interesting adaptation to an environment with rising temperatures, it hasn't really helped "us" much. So how has cloning of mammals helped us? The field is new enough that most Americans haven't yet experienced any remarkable improvements in their lot from cloning, but this may soon change. The field where cloning has originated is agriculture, where one of the challenges since we first domesticated animals has been to create livestock which are more productive (more meat, more milk, more fur, etc.) The greatest challenge has been to create breeds of livestock which reliably transmit productive characteristics. As a result, we've got Hereford cattle (which have high muscle mass) and Jersey cattle (which produce large amounts of milk). These breeds do have higher levels of production on average, but there is still significant variation within breed. If you've ever been to a rural county fair, you've seen the judging competitions for livestock. What if you could just clone the prizewinning livestock and avoid the messiness of breeding for the best possible combination of traits? The practice of cloning isn't yet reliable enough to produce herds of identical super livestock more efficiently than doing it the old fashioned way by breeding the prizewinners. On the other hand, it is possibly a more efficient way to expand herds of genetically altered livestock, which have been created to produce therapeutic proteins in their milk. In the meantime, cloning has helped us understand some of the basic biology of aging and cellular differentiation. One of the models for aging held that the length of structures at the end of chromosomes known as telomeres is one of the clocks regulating the aging of an organism. Older cells do have shorter telomeres. However, the fact that we can experimentally reverse this process in clones suggests that the shortening of telomeres is not the simple, inexorable process we thought it was. This remains one of the hottest areas of cloning research. The revolution of nuclear transfer technologies is that if you take a nucleus out of a cell from a somatic tissue of a fully grown organism you can reprogram it to behave as if it were the nucleus of an undifferentiated fertilized egg. This has fascinating implications for producing replacement tissues: some organs like the liver are capable of regeneration, while most other organs cannot. What if we could grow a new kidney for people who need one? If we can take a fully differentiated cell all the way back to an undifferentiated state where it can grow into an entire organism, perhaps we can reprogram it to grow into a kidney. Thousands of people die every year waiting for tissue matched donor organs, so if we can figure out how to artificially produce replacement organs through a process similar to cloning, we could save thousands of lives per year. I hope this begins to answer your question. Chris Carlson
Try the links in the MadSci Library for more information on Genetics.