Thursday, April 9, 2009
Pigeons
On page 54, Carroll discusses the white rump of feathers between the base of the tail and the lower back on pigeons. The pigeons with the white rump made up 20% of the pigeon population but only 2% of the pigeons attacked by falcons. The white rump pigeons were targeted less and could escape the predators better then the normal pigeons. It is discussed that the white rump may be a distraction, and the white rump has happened through a mutation. What is another example of how a mutation has helped an organism? Is the organism going through natural selection due to this mutation such as the pigeons? Have any mutations helped humans, and can we see natural selection beginning to take place as well?
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The basic process of natural selection is if a mutation provided a selective advantage, or "helped an organism," the organism would be more likely to survive and reproduce, thus keeping the selective advantage within the genome. If a mutation in any way disadvantages the organism, it is less likely to survive or reproduce, so the trait does not get passed on to further generations.
ReplyDeleteIn the case of the pigeons, the mutation that caused the white rump resulted in the pigeon being much more likely to survive a falcon attack. As a survivor, it reproduces and spreads the genetic information for this selective advantage. The survival of this trait throughout generations allows it to be observable by humans, only because it provided an advantage in the first place. Ultimately, this shows that all traits that are comparable to the species without the specific mutation must be advantageous (or at least, is not a disadvantage) to the species in order for it to remain within the population. Examples of "how a mutation has helped an organism" is present in basically every organism, but a specific example is the ice fish, which Carroll also mentions in his book. The blood of ice fish has undergone many mutations throughout the generations to become free of red blood cells. This has allowed the adaptation of the ice fish to the freezing temperatures of the Antarctic, increasing their survival. A human example of natural selection is sickle-cell anemia. In African regions where the risk of malaria is extremeley high, the mutation of red blood cells that results in sickle-cell anemia can be advantageous. Carriers of the mutation have a much higher resistance to malaria, so in these areas, the mutation allows these people to live longer and reproduce more, keeping the mutation within the genetic information of much of the population.
The most frequent and rapid mutations that help organisms can be seen in many bacteria. As bacteria reproduce very rapidly, many mutations occur during the replication, translation, and transcription process. These rapid mutations allow some bacteria to grow resistance to antibiotics that used to threaten their survival. These genetic mutations that grow immunity to antibiotics are a great selective advantage to the bacteria. Antibiotics kill bacterial cells by disrupting their function. The antibiotic binds to a protein so that the protein cannot function properly. The proteins usually involved in the copying of DNA, making proteins, or making bacterial cell walls are inhibited, preventing the important functions for bacterial growth and survival. When bacteria have a mutation in the DNA that codes for one of the proteins that antibiotics disrupt, the antibiotic cannot bind to the mutated protein and the mutated bacteria gain a selective advantage and survive to reproduce and pass on their mutated genes to future generations, passing along the resistance.
ReplyDeleteThe bacteria are definitely going through natural selection in the process of growing resistance to antibiotics. The natural selection of the bacterial genes can be most easily distinguished, since bacterial cells reproduce very rapidly. This expedites the genetic inheritance of the mutated genes that have resistance to bacteria, and speeds up the mutation rates of further generations, causing bacteria to constantly mutate and have selective advantages or disadvantages that contribute to natural selection. The advantageous mutations are selected for the organism and disadvantageous mutations are selected against and eventually fossilized. The increased use of antibiotics today contributes to the rise of antibiotic-resistant bacteria, since the antibiotics provide a stimulus for bacterial genes to mutate and grow resistance. About 70 percent of bacteria that cause infections in hospitals are resistant to at least one of the drugs most commonly used to treat infections. This shows that as more antibiotics are used, bacteria develop advantageous mutations against the treatments, and pass on their resistance to their daughter cells. Staphylococcus aureus is one of the major antibiotic-resistant pathogens that was the first bacterium to grow resistance to penicillin. Even though stronger antibiotics are being used, this causes the evolution of even more resistant bacteria that survive and reproduce. Therefore, it is a great selective advantage to the bacteria since they are capable of surviving and reproducing to pass on their genes.
The mutations of humans that differentiated humans from other primates from their common ancestors have provided huge selective advantages, since humans are on the top of the food chain, allowing their survival and reproduction. Large brains and the ability of homo sapiens to walk on their feet rather than on four legs allow humans to use their hands for other tasks such as eating, learning, writing, etc. The large brains of humans allow humans to be the most intellectual organism in the world, leading to the understanding of the world and the survival of the organism by exploiting the world. Humans have the brains to control stronger animals such as lions. Natural selection is not as easily seen compared to bacteria, since humans to do not replicate every couple of minutes. However, slight changes in phenotypes of future generations show that genes are changing with various mechanisms such as mutation and crossing over. The superiority of homo sapiens to other organisms and primates show that the large brains are a selective advantage that can lead to natural selection of humans to have even larger brains or brains with greater folds for intellect. However, the process of natural selection cannot be completely assured, since humans do not reproduce rapidly so the process is very slow. The actual phenotypic change due to various mutations and natural selection cannot be distinguished.
http://www.fda.gov/Fdac/features/795_antibio.html
http://www.answersingenesis.org/articles/am/v2/n3/antibiotic-resistance-of-bacteria
With the advent of artifical fibers and the subsequent decrease in natural fibers used in ropes such as cotton and hemp, factories have been spewing out waste products that were inpalatable to the bacteria living in the waste waters. Since the invention of nylon in the 1940s,a bacterium called Pseudomona has developed enzymes that break down the nylon oligomers by breaking the nylon linkages. As these linkages are not naturally found in nature, the enzymes were produced via mutation. These enzymes are the result of frameshift mutation from a gene that codes for an unrelated enzyme. With nylon oligomers as a suddenly abundant food source, it is a selective advantage to have this mutation as this new food is readily available in high concentrations. This change has been repeated with non-nylon-metabolizing strains of Pseudomonas in the lab with nylon oligomers as the main food source with the mutation appearing after few generations, indicating natural selection.
ReplyDelete700 years ago, the Black Plague was sweeping the world, killing 1/3 of the population. Yet some people in the hardest hit areas survived because of a gene mutation that prevented the disease from entering their white blood cells. Obviously a selective advantage in those times, biologists now have traced a mutation in the CCR-5 receptor gene that appears to protect against HIV as being the same mutation that protected humans against the bubonic plague. People with two copies of this gene mutation are immune to HIV and those with one copy are still suseptable, although the disease progresses more slowly. With no know cure for HIV, the presence of this mutation is a selective advantage for those exposed to the HIV virus.
http://www.gate.net/~rwms/EvoHumBenMutations.html
http://www.pbs.org/wgbh/evolution/library/10/4/l_104_05.html
Mutations can be both beneficial and it can be a disadvantage in some cases. A prime example of a mutation that could be beneficial for the organisms could be found in the book on page 52 and peppered moths. In the industrial revolution there was a lot of pollution in England and North America. The pollution altered the “coloration and lichen growth on trees where the peppered moths rested” (Carroll 52). This pollution drastically altered the moths’ environments. With dark environments the population of the moths called for natural selection. In darker environments there the moths that contained more melanin were harder to spot by predators because they were blended in with the environment. This called for the moths with low melanin or lighter moths to be easier to spot by predators. Soon as predators feasted on the light colored moths, the dark colored moths were blending in with the environment as the dark form of the moth accounted for almost 98 percent of the total population in some areas of England. Soon after the industrial revolution, clean air laws were forced into effect lowering the amount of emissions into the air and cleaning up the environments. This however was a disadvantage towards the dark moths as cleaner air meant lighter environments and dark moths were once again easier to spot for predators. Soon the population of the dark colored moths drastically decreased “from about 90 percent in some areas to about 2 percent”(Carroll 52). In conclusion the environment in which the moths resided in determined the rate of survival.
ReplyDeleteAs for humans not all people that are exposed to malaria get life threatening health problems. Malaria is one of the major causes of death in Sub-Saharan Africa. Researchers at the University of Toronto have found that some people that have a mutation in the human gene are not susceptible to this disease. The researchers found that a deficiency in an enzyme called pyruvate kinase, which is required for energy production in the body, provides protection against malaria infection.
http://www.eurekalert.org/pub_releases/2008-04/uot-mih042108.php
An example of a mutation that has actually helped an organism would be the so called Panda’s “Thumb”. Although controversial, the fact that giant panda is a close relative of the bears is widely accepted. The key mutation that occurred with the pandas is within its paw. The panda’s thumb is not a real thumb as it is a bone inside the paw. When compared with a bears’ paw, the panda has its “thumb” where the bear has its radial sesamoid. Sesamoid bones are little bones that are contained within a ligament that provide strength and leverage to the ligament for it to be flexible and reduce constant tearing. A panda’s thumb is an enlarged sesamoid bone. The panda’s main diet is bamboo, and it is very difficult to break the stalks of the bamboo. The enlarged bone within the paw of the panda helps to grasp the bamboo. Over the years, the Panda has evolved and due to natural selection has enlarged the sesamoid bone and instead of using it with a tendon to increase its mechanical effect, the panda has slowly evolved the bone into a use in handling the bamboo better. A similar bone also is found in the leg of the panda. This is also an enlarged bone that is the same location that the radial sesamoid is in the hand. The bone, tibial sesamoid, is also prevalent in other bears, but in pandas this bone also is bigger. There are 2 theories which constitute to why the bears have the enlarged bones. One story is that the radial sesamoid that was in the paw was initially to strengthen the tendon, but instead it got bigger to help the panda with the grip on the bamboo. The tibial seamoid also got enlarged because of that because of consequence of the bone development in the paw. Another story is that the radial and sesamoid bones were both used to strengthen the tendons, but then they got bigger as a result of the ancestral panda’s climbing habits. The radial tendon was then used for bamboo as a consequence. The panda went through evolution and mutation of the species. It is very sad today to see that these panda’s are becoming extinct.
ReplyDeleteAs for humans not all people that are exposed to malaria get life threatening health problems. Malaria is one of the major causes of death in Sub-Saharan Africa. Researchers at the University of Toronto have found that some people that have a mutation in the human gene are not susceptible to this disease. The researchers found that a deficiency in an enzyme called pyruvate kinase, which is required for energy production in the body, provides protection against malaria infection.
http://en.wikipedia.org/wiki/The_Panda%27s_Thumb_(blog)
http://www.simonsingh.net/The_Pandas_Thumb.html
http://www.athro.com/evo/pthumb.html