Monday, April 6, 2009
The Evolution of Genes that Have Simmilar Effects, but Different Amino Acid Sequences
On page 154, Carroll discuses how four different venoms, from four different animals of four different phyla, evolved to function in the same way, even though their amino acid sequences differed. Discuss other examples in which multiple animals evolved to have genes that all produced a similar result, even though the amino acid sequences differed. Also discuss the environmental stressors that led to the said gene being a selective advantage.
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ReplyDeleteA lot of Ecologists say that Antartica is a great place to study Evolution. They say that Antartica's freezing temperture has contributed to the evolution of various organisms. From here, we can see different organsms with different genetic code developing same result to survive in harsh weather.
ReplyDeleteOn page 151, Sean Carroll gives another example which multiple animals evolved to have gene that all produced a similar result. Sean Carroll discusses Arctic fish and Antarctic fish because they both have different sequences of genes for making antifreeze yet they serve the same purpose: to survive in freezing temperature.
For example, Arctic cod, living in Artic Ocean has developed Antifreeze protiens identical to those of Notothenioids. They are not related but they are still making the same Antifreeze protiens. This evolutionary process is called Convergent Evolution.
Another animal that uses ‘Antifreeze’ is wood frogs. They have different way of surviving in freezing temperature. When the winter gets close, wood frogs start to build up Urea in their body system to reduce the ice formation in the body.
In addition, Antartic Tooth fish alsomakes glycoproteins that helps its blood not freeze in cold water. It also has really slow heart beat.
As we can see from Artic fish, Antratic fish, and wood frogs, animals develop different styles of surviving according to its natural surroundings. Even though they have different genetic sequences, they are all doing the same work. From this, we can learn that animals develop their specific skills by natural selection or environmental stressors. This evolutionary process is called Adaptation.
Many biologists point out that the example of Artic fishes developing Antifreeze is Adaptation. Adaptation happend in two stages. At first stage, some kind of mutation occurs which gives certain species a power to survive and pass on their genes. Second stage is when that population of new species increases over many years and other species die out. In the laguage of Ecology, the expansion of this new species is called Adaptive radiation.
As the book says, the evolution’s key ingredients are “chance, selection, and time. The use of Antifreeze of wood frogs, Antrartic fish and Arctic fish shows those key ingredients of Evolution because these three distinct animals developed same ‘skills’ by chance, natural selection, and time.
Source: http://www.myexploratorium.com/origins/antarctica/ideas/fish4.html
http://icestories.exploratorium.edu/dispatches/antarctic-projects/antifreeze-fish/
Mark is most likely talking about the evolution of the venom containing potassium channel blockers that affect the passing of electrical signals among neurons and muscles. This venom individually developed in sea anemones (cnidarians), scorpions (arthropod), marine cone shell snails (mollusk), and black mambas (vertebrate) while surprisingly other close relatives of these species do not have this particular venom. The development of this particular venom in each species probably serve different purposes such as protection as well as predation and leaving prey or aggressors immobile.
ReplyDeleteAnother example of convergent evolution is the development of hinged jaws in the two phylum Arthropoda and Chordata. Arthropoda being one of the most successful animal phyla can be partially contributed to their development of jointed appendages. One of these specialized appendages are the jawlike mandibles. Although these mandibles are not actually classified as jaws, they function in biting, cutting, holding, and chewing food similarly to jaws in phylum Chordata. Over the evolutionary process hinged jaws developed in these two phyla while having some differences. In phylum Arthropoda the mandible is useful in mechanical digestion as well as pushing food through the organism’s mouth. Crustaceans have specialized mandibles with molar and incisor processes and other animal in phylum Arthropoda such as many different species of insects have mandibles specialized for their particular lifestyle needs. Carnivorous beetles for example have extended mandibles for seizing and crushing prey, that have adapted specifically for killing prey, while caterpillars have mandibles specialized for cutting leaves. In phylum Chordata, the hinged jaw is different from phylum Arthropoda in that it is a single, nondividing structure that similarity functions mainly in mechanical digestion.
Vertebrate jaws were one of the most important developments in vertebrate history as it greatly increased the amount and diversity of food options, leading to the vertebrate’s dominance. Vertebrate jaws evolved from the modification of the skeletal rods that supported the anterior pharyngeal slits that were once used for suspension feeding but became obsolete. The mandibles of Arthropoda developed differently from the ancestral legs of insects that became jointed appendages specialized for digestion processes. While these two types of hinged jaws developed entirely differently and individually in each of the animal phyla, they developed to a similar result or necessity. The hinged jaws of Arthropoda and Chordata both function in mechanical digestion and greatly increase food options throughout each environment, allowing these hinged organisms to live in areas that might not have a great diversity of food options. As well the ability to tear portions of a large meal is a very simple but important primary task in digestion. The biting action of hinged jaws can create practical portions of food for effective digestion, and because the hinged jaws are the first structure in digestion, the mechanical digestion can be accompanied by chemical digestion in the mouth. The newly formed area contains the necessary surface area for enzymes in perhaps saliva to act first on the food. As well the hinged jaws are a specialized way of food selection and digestion as the jaws are can selectively be used to choose what items to digest compared to organisms that do not have hinged jaws that cannot isolate substances from entering the digestive tract. The energy necessary to eliminate potentially toxic materials in the body can take a toll in health as well as dispersion of valuable energy. Another advantage of hinged jaws is the amount of energy now accessible from the environment. The ability to digest many different types of organisms in that particular environment increase the amount of energy attainable in Arthropoda and Chordata as energy needs must be met for a more complicated body structure. All these benefits of jaws make them indispensable to the organisms and a viable goal of the evolutionary process.
Furthermore other examples of convergent evolution can occur from the duplicative process of genetic material discussed by Carroll in page 106. He uses the example of opsin genes duplicating and then developing differently through evolutionary selective processes. Particular opsin genes code for different ranges of maximum absorption which differs extremely between organisms on land or water surfaces and organisms in deeper depths. Mutations in the opsin gene for animals in deeper depths have a maximum absorption of a shifted range of under 500 nm because in the deep ocean less light penetrates the water. The shift of the opsin genes have evolved individually in many different species such as the bottlenosed dolphin, pilot whale, John Dory’s fish, and various eels that need a lower shift in maximum absorption for their particular environment.
http://dic.academic.ru/dic.nsf/enwiki/6072873
http://books.google.com/books?id=sKT2Sq4P0j8C&pg=PA403&lpg=PA403&dq=hinged+jaws+evolution&source=bl&ots=Y1MrZkU4xF&sig=UlHAxgGWdjVTgpTGJgArBBvzPfs&hl=en&ei=S63iSaDtGpjsnQeHsqWzCQ&sa=X&oi=book_result&ct=result&resnum=1#PPA403,M1
http://www.fiu.edu/~longoria/gly1101/mammals.pdf
Opsins are a group of light-sensitive 35-55 kDa membrane-bound G protein-coupled receptors of the retinylidene protein family found in photoreceptor cells of the retina. Five classical groups of opsins are involved in vision, mediating the conversion of a photon of light into an electrochemical signal, the first step in the visual transduction cascade. Another opsin found in the mammalian retina, melanopsin, is involved in circadian rhythms and pupillary reflex but not in image-forming. The two types of opsins, type 1 and type 2, are similar in structure and function, but they evolved independently from one another in bacteria and animals. Like eukaryotic opsins, prokaryotic opsins have a seven transmembrane domain structure similar to that found in eukaryotic G-protein coupled receptors. Several type 1 opsins are used by various bacterial groups to harvest energy from light to fix carbon using a non-chlorophyll-based pathway. Additionally, sensory rhodopsins exist in Halobacteria that induce a phototactic response by interacting with transducer membrane-embedded proteins that have no relation to G proteins. Two families of vertebrate opsins are generally recognized due to different spatial expression and evolutionary histories. Rhodopsins, which are used in night vision, are high-sensitivity, low-acuity opsins found in the rod photoreceptor cells. Cone opsins, employed in color vision, are low-sensitivity, high-acuity opsins located in the cone photoreceptor cells.
ReplyDeleteOpsin proteins covalently bind to a vitamin A-based retinaldehyde chromophore through a Schiff base linkage to a lysine residue in the seventh transmembrane alpha helix. In vertebrates, the chromphore is found in the retinal binding pocket of the opsin. The absorption of a photon of light results in the photoisomerisation of the chromophore and this induces a conformational change in the opsin protein, causing the activation of the phototransduction cascade. Opsins are functional while bound to chromophores. These opsins and chromotophores allow for primates, humans, and other vertebrates to form vision. The environment that the species lived in required vision for the hunting and preying of food, thus, resulting in the formation of opsin proteins and chromotophores that allow the retina to form vision. Some primates and humans have trichromatic vision, allowing more selective advantages. The trichromatic vision allows primates to detect food, mates, and danger with visual cues, increasing their survival rate. Bacterias use opsins to harvest energy from light to fix carbon using a non-chlorophyll-based pathway, increasing their survival rate and means of getting energy. This became a selective advantage in bacteria, and opsin proteins came from mutated genes that were selected for and preserved due to the greater survival rate and natural selection.
http://en.wikipedia.org/wiki/Opsin
http://www.britannica.com/EBchecked/topic/116032/chromophore