On page 147, Dr. Moalem introduces the term "junk DNA," which describes the noncoding DNA that makes up about 70% of human DNA. This relates to Big Idea 3 (Living systems store, retrieve, transmit, and respond to information essential to life processes) since DNA is the method through which all information that provides information for cells is transmitted, and "junk DNA" is still a portion of DNA that contains information, though it is not currently being translated into proteins. Dr. Moalem connects the idea of junk DNA to jumping genes by recognizing that up to half of junk DNA may be made up of jumping genes.
How did Dr. Moalem say that jumping genes came to be embedded into human DNA? What was the junk DNA's original "use?" Why is it no longer "used?" Connect this back to evolution. Do jumping genes benefit the individual or the population and why? Why does the amount of junk DNA an organism have tend to correlate with how complex it is?
Are there any similarities between what Dr. Moalem said about junk DNA and what Sam Rhine said at the Genetic Update Conference?
Austin Hua (auhua4@students.d125.org)
Jumping genes are intentional mutations in response to environmental changes that cause whole sequences of DNA to move from one place to another, and even insert themselves into active genes. Dr. Moalem says that jumping genes became embedded in human DNA because they helped some species adapt their way through periods of significant change that were brought about by large environmental shifts. These jumping genes might have increased genetic variation and even improved survivability or adaptability in species during these times of change.
ReplyDeleteJunk DNA is all of our noncoding DNA, because it doesn’t contain the genetic code to build any cells directly. Scientists noticed that large portions of this noncoding DNA, almost half of it, is made up of jumping genes. Scientists also noticed that this junk DNA greatly resembles a special type of virus called a retrovirus. Originally, this junk DNA served as a retrovirus that became permanently encoded in an organism’s DNA because the retrovirus writes itself into the DNA of cells in the germ line of an organism that is passed to an organism’s offspring. However, these retroviruses became part of the junk DNA because if the virus doesn’t hurt, or even helps, the offspring’s chance to survive and reproduce, that virus may end up a permanent part of the gene pool, or the noncoding junk DNA. This connects to Darwin’s idea of evolution, because if the virus didn’t harm the organism, then the virus became permanent in the gene pool because it helped “enhance their survival and reproduction in specific environments.” (Campbell, 456)
Jumping genes are beneficial to the population in some cases because these genes “can help us adapt to new situations, but the randomness of the movement can also have unintended negative side effects.” (http://minnesota.publicradio.org/display/web/2012/03/15/daily-circuit-brain-science) This differentiation allows adaptation to occur over time, allowing humans to better survive and reproduce. However, jumping genes were originally seen as negative to the organism. For a long time “it was thought that these elements existed solely for their own purpose, taking advantage of the host’s transcriptional machinery while causing detrimental effects to the host.” (http://www.thefreelibrary.com/The+'evolution'+of+a+PhD+project--from+jumping+genes+to+biochemical...-a0171539429) These highly repetitive elements were seen as almost parasitic to the organism. Now, “scientists have seen that some other advantageous phenotypes, such as resistance to the insecticidal toxins from Bacillus thuringiensis in the tobacco budworm, Heliothis virescens, have evolved due to the insertion of a jumping gene into the cadherin gene of this organism.” (http://www.thefreelibrary.com/The+'evolution'+of+a+PhD+project--from+jumping+genes+to+biochemical...-a0171539429)
Separately, the amount of junk DNA an organism has tends to correlate with how complex it is. Although junk DNA is considered noncoding, it may at one point have been able to code information. So, the more accumulated junk DNA an organism has, the greater the extent of their ability was to encode proteins. However, while overall genome size, and by extension the amount of noncoding DNA, are correlated to organism complexity, there are many exceptions. This relates to what’s known as the C-value Paradox, which is the observation that genome size does not correlate with organismal complexity; for example, some single-celled protists have genomes much larger than that of humans.
ReplyDeleteThe topic of junk DNA was discussed in Sam Rhine’s Genetics Update Conference. The idea of junk DNA relates to Big Idea 3 (Living systems store, retrieve, transmit, and respond to information essential to life processes) since DNA is the method through which all information for cells is transmitted, and "junk DNA" is still a portion of DNA that contains information, though it is not currently being translated into proteins. Sam Rhine and Dr. Moalem both addressed junk DNA; Rhine stated that about “1.5% of the human genome is made up of coding' DNA, which carries a DNA Code of 21,000 protein producing genes. This means that about 98.5% of the human genome is made up of noncoding DNA, or junk DNA.” (Sam Rhine, 4) Speaker Sam Rhine also addressed the concept of the genome versus the epigenome, which relates to the idea of jumping genes purposely modifying our genes. Same Rhine stated that “modification is an ongoing, life-long process, affected by the environment.” Our genome is stable despite our changing environment, whereas our epigenome is fluid and changes all the time. These epigenetic modifications can be passed through the gem line, similarly to our noncoding junk DNA.