Tuesday, April 14, 2009
DNA and Evolution
Carroll refers to DNA to show support for evolution throughout the book. He repeatedly states that "our DNA shows our evolutionary history." If that's so, why can't we easily track the evolution of a specific organ or characteristic in modern day organisms? If all the answers are in the DNA, why don't we have them yet?
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We can't get all the answers from DNA because we do not have the DNA of all the organisms through out history. If we had a way of getting the DNA of every organism that existed in say the previous 1 million years, then it would be much easier to track their evolution. But because we only have pieces of the DNA puzzle from various organisms, we can only figure out so much.
ReplyDeleteSecond of all researching and deciphering genetic code is no simple task. In a sense it is figuring out one huge puzzle, or metaphorically speaking the "Great puzzle of life". Things of great importance take great amounts of time to accomplish, otherwise the thing itself would not be "great". And on top of that, dedicated research to this topic has mainly been in the last 50 years, with the last 20 years getting any real steam. But say 100 years from now, we might have a much larger library of information and being closer to answering "all the questions".
Well, although you may not believe it, there is still a lot left to discover about DNA. Our knowledge of DNA so far is very limited, although we do believe that "our DNA shows our evolutionary history" there is a lot left in DNA that we still don't understand, which explains why we can't simply track evolution. Although the Human Genome Project successfully sequenced the Human DNA, the function of most of our DNA is still unknown. If we could somehow figure out how the exact sequence of DNA affects each part of an organism, then so much would be revealed to scientists, and these questions would be answered.
ReplyDeletePartially Deepak, it is a matter of time for scientists to track the genetic basis of a certain trace across phylogenic levels. For one, many more organisms need to have their genomes sequenced in order to have a sufficient database in order to find similarities and differences that point to the work of evolution. As PCR and other in-vitro DNA replication methods become more efficient, DNA sequencing will get faster and faster so that this process is greatly speeded up. From there, it is only the application of current taxonomic knowledge to determine which animals are the most closely related. After that, a genetic comparison can be initiated in order to determine what specific changes in the genetic code caused the change in specific traits. Also in order to do this, there needs to be a greater of understanding of what each gene codes for and how exactly they interact in order to form specific organs or characteristics.
ReplyDeleteThe most convincing genetic basis for evolution is the presence of specific junk DNA such as LINES in SINES. These types of junk DNA, once created in a species, is then passed down to all species that evolve from the original species because natural selection does not work on non-transcribed DNA. This is one of the most crucial genetic explanations for evolution, but in time the specific evolution of certain organs will be able to be tracked genetically once a greater database of genetic knowledge is assembled.
What Carroll means by his quote is that by examining the DNA record of different species, we can note similarities and differences between the species, and from that information, we can deduce the relationship between the species. However, as Boris pointed out, the reason why we cannot determine the exact evolutionary history of any species is because we do not have knowledge of the DNA of the ancestors. For example, the common ancestor of two species, such as humans and chimpanzees, no longer exists, because evolution split that ancestor up into different groups, includinmg humans and chimpanzees. Therefore, we do not know the exact DNA information of the ancestor, and cannot directly determine the evolutionary tree. however, by comparing human and chimpanzee DNA, we can note similarities in genes. This allows us to deduce that the common ancestor of humans and chimps also had that DNA sequence. It is every evolutionary biologists dream to find the DNA information of the LUCA (Last Universal Common Ancestor), but sadly this is not available. While the limited genetic information we have is not perfect, Carroll makes the point that by using the genetic information we DO have, we can find out a lot about the origin of species. By using techniques such as genetic landmarks (LINES and SINES), we can find genetic similarities between species. Genetic information has allowed us to identify humans' closest relatives, as well as relations between many other species. As technology and biologic information increases, we will be able to use genetic information more effectively to determine relationships between species and attempt to fill in the vast chasm that is the evolutionary pathway of life.
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