Tuesday, April 7, 2009
different paths to similair ends
On pages 146-147 Carroll discusses how Jianzhi Zhang had found groups of monkeys in both Africa and Asia that evolved rumination. When taking a closer look into the similarities of the different monkeys from different parts of the world, Zhang found that "the duplication of ribonuclease genes occurred at different times and produced different numbers of ribonucleases...several of the exact same changes subsequently occurred." Even after calculating the probability in which this same mutation would occur they found that it was a slim chance. Discuss how these almost identical changes occurred at two different locations a two unconnected monkey species. Include information on the probability of a certain mutation occurring(57-62) and how natural selection plays a role in allowing this all to happen. Also discuss when fossilization of a gene occurs in different species at different times and give examples. Connect both of the above to the theme of interdependence of nature and how the surrounding environment may have manipulated these changes.
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These similar outcomes in the different species of monkeys and even in cows occur because of the spectacular process of natural selection. As Carroll writes, natural selection’s job of “[fine-tuning] the enzymes to the more acidic environment of the monkey’s foregut” combined with the process of fossilization and relaxed selection is what caused these changes (147). Both of these species of monkeys lived in an environment in which it was beneficial and maybe even necessary to develop this process of breaking down nutrients from leaves and bacteria in a specific way. Adaptive evolution is strongly suggested by one type of protein having a strong association with a specific environment. The pancreatic ribonuclease is necessary for digesting large amounts of RNA derived from the symbiotic microflora of the foregut of these monkeys. The foregut has a very acidic environment and therefore the enzymes and proteins had to adapt as well in order to maintain the same processes that are vital for the monkeys and to not become denatured. Probably because of foregut fermentation and related changes in digestive physiology, the pH in the small intestine of colobine monkeys shifts to 6–7.
ReplyDeleteSo, slowly over time, the enzymes changed to accommodate for their acidic environment. The role of stomach lysozyme is to break open the foregut bacteria so that their contents are accessible to pancreatic ribonuclease and other digestive enzymes of the host. Stomach lysozymes from ruminants and colobines appear to have adapted to their new role through convergence of protein sequence and function. But in actuality, it is not that radical to believe that this identical change had been brought about by similar mutations and natural selection. The gene was duplicated in both the species, which is a common mutation to occur accounting the thousands of years that the gene had to be mutated. The per site rate of mutation averages about 1 per 500 million bases in DNA in most animals, according to Carroll, so knowing that millions of years had passed and the mass number of individuals of both monkeys that the mutations could have occurred in, it is not so improbable that identical mutations had arisen in the same species by chance (156). It was just a coincidence that both species’ environments put them in a position where this mutation was actually favorable. Sexual selection then favored the monkeys which had this adaptation and eventually it was passed so that virtually every monkey in that species has this specialized pancreatic ribonuclease that will help the monkeys survive and therefore reproduce in the future.
http://www.researchgrantdatabase.com/g/5R01GM047474-03/MOLECULAR-BASIS-FOR-EVOLUTION-OF-FOREGUT-FERMENTATION/
http://www.biology.emory.edu/research/Yokoyama/pdfs/yokoyama2002a.pdf
http://74.125.95.132/search?q=cache:8zb6Sbg-wV0J:helix.mcmaster.ca/4dd3/4DD3_Mar9_2009.pdf+foregut+ribonuclease&cd=10&hl=en&ct=clnk&gl=us&client=firefox-a
Aspergillus oryzae Ribonuclease T2 is a member of the RNase T2 family of endonucleases that are present in a wide variety of microbial, plant and animal species. In contrast to Aspergillus oryzae Ribonuclease T1, ribonuclease
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