Sunday, April 5, 2009
puffer fish and humans
Carroll compares the genes in the DNA of puffer fish and humans finding 7350 genes that are similar within the two species and that the proteins that these genes code for are on average 61% identical. With this comparison it can be seen that it is not a mere coincidence but that immortal genes play a role in creating a core set that is required for survival. Discuss what these genes are and how they have survived throughout history. It also discusses that they are not prone to mutations. Discuss how the genes have adapted to mutations and the variety that now exists for certain genes. Give specific examples of immortal genes and discuss their purpose and why they are so crucial. Discuss what qualities these genes may play in survival in species that are so different and live in completely different environments [ puffer fish compared to humans].
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ReplyDelete“Immortal” genes are genes that have endured over eons of time and resisted the various mutations that species have gone through. They have survived throughout history due to the “preservative force” of natural selection. The mutations that cause selective advantages are changes that occur in narrow limits in the genome of organisms described by Carroll as “running in place” (Carroll 72). The 7350 genes that are shared between the puffer fish and humans provide evidence that all organisms originated from a common ancestor.
ReplyDeleteThe immortal genes are not immortal in that the DNA are exactly the same. The immortal genes are, in fact, prone to mutations. They are immortal in that the gene endures. The individual letters of the gene are prone to mutations, but the repetition of the genetic code prevents harmful changes in the gene. Synonymous changes are changes in the genetic code that do not alter the encoding of an amino acid. The nature favors the synonymous changes to nonsynonymous changes in a ratio of 3:1, allowing the endurance of immortal genes. Humans also adapted to mutations by noncoding DNA. By having vast amounts of noncoding DNA, the probability of mutations occurring in the coding DNA are reduced. As can be seen in Figure 3.3 in page 81, different bases can code for the same gene in various organisms. The amino acid leucine, for example, has various DNA triplets that code for the specific amino acid such as TTA, TTG, CTA, CTT, CTC, and CTG (Carroll 82). These different triplets can exist in different organisms, but they all code for the amino acid leucine.
The 14 individual amino acids that all proteins are made out of have survived eons of time and have been maintained throughout evolution. The 14 amino acids make up all proteins that are crucial in the survival of all organisms. Proteins account for more than 50% of the dry weight of most cells and are used for structural support, storage, transport of other substances, signaling from one part of the organism to another, movement, and defense against foreign substances. Also, proteins regulate metabolism by selectively accelerating chemical reactions in the cell as enzymes. All organisms need enzymes to catalyze internal chemical reactions (Campbell, Reece 71).Enzymes play crucial roles in metabolic pathways by lowering the activation energy and allowing reactions to occur in lower temperatures or with less energy. Cellular respiration, for example, uses enzymes hexokinase, isomerase, and kinases during the glycolysis stage. Proteins carry oxygen necessary for cellular respiration, build tissue, copy DNA for the next generation, and much more.
These immortal genes can play crucial roles in the survival of species that are very different by providing the essential proteins that all organisms need to survive. All puffer fish and all humans require the 14 individual amino acids to code for specific proteins. The triplets that code for the 14 amino acids may be different, but the 14 amino acid genes are immortal. There have been various mutations, but the mutations have been continuously purged by natural selection and the genes have survived.
http://occawlonline.pearsoned.com/bookbind/pubbooks/campbell6e_awl/chapter9/deluxe.html
Sunday, April 5, 2009
ReplyDeletepuffer fish and humans
Carroll compares the genes in the DNA of puffer fish and humans finding 7350 genes that are similar within the two species and that the proteins that these genes code for are on average 61% identical. With this comparison it can be seen that it is not a mere coincidence but that immortal genes play a role in creating a core set that is required for survival. Discuss what these genes are and how they have survived throughout history. It also discusses that they are not prone to mutations. Discuss how the genes have adapted to mutations and the variety that now exists for certain genes. Give specific examples of immortal genes and discuss their purpose and why they are so crucial. Discuss what qualities these genes may play in survival in species that are so different and live in completely different environments [ puffer fish compared to humans].
Answer:
One of the main reasons that we find so many of these "immortal genes" amongst different organisms is because of the similar functions we all need in order to survive. Carroll provides an example of a function that all living things need like, "the decoding of DNA and RNA and the making of proteins" (79). These regular cellular functions that almost all cells perform are necessary in every living organism and if a mutation occurred to one of the genes that contain the instructions to the cellular functions and processes, the organism would not survive because it would not be able to do the proper functions to maintain life. This powers natural selection in weeding out all of the organisms with mutated “immortal genes” so each generation’s organisms maintain the same fundamental genes. These sequences of genes that program our bodies to perform these functions are critical to our survival. These "immortal" genes NEED to stay the same amongst the species, because without them then life would cease to exist. That doesn't mean though that amongst every species these strands of immortal genes are exactly the same, because they are prone to mutation too. They serve the same purpose and can perform the same function because the body has been created to protect these genes. Certain genes that code for such things as enzymes for replication, transcription factors, sodium-potassium pumps, and microtubules for other cell division are also vital to the life of all organisms.
One gene that has stayed nearly the same in all species is the Pax-6 eye-building gene. This gene is the main gene that controls the development of the eyes, sensory organs, and neural tissues that relate to sight. This gene is expressed in the developing nervous system, and in developing eyes. Mutations in this gene are known to cause ocular disorders such as aniridia and Peter's anomaly. Only six amino acids differ between the Pax-6 gene in fruit flies and mammals, and the gene is the exactly the same in both mice and humans. The reason why this gene has been preserved between millions upon millions of species is that almost every species, especially terrestrial species, needs eyes. Eyes are necessary in getting food, finding mates, and avoiding predators. Also, eyes with trichromatic vision are especially important in animals with a high proportion of fossilized olfactory genes, such as humans. Some animals, such as a few burrowing animals and fish that live at very large depths of the ocean, don’t need eyes since they would be unnecessary in such dark environments.
http://en.wikipedia.org/wiki/PAX6
http://www.genecards.org/cgi-bin/carddisp.pl?gene=Pax6
http://www.biomedcentral.com/1471-2350/5/9