Monday, March 9, 2009
Prompt III
Genetic diseases are found in all human populations. Some diseases such as Tay-Sachs disease and sickle-cell disease occur more frequently in certain populations such as Ashkenazi Jews and African Americans respectively. Does this phenomenon indicates that the genetic mutations for these particular diseases occurred in our hominid ancestor or that the mutation arose independently after the human race had diversified?
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I think that each of these genetic diseases developed at different times along the timeline of evolution. Certain diseases that are occuring in all ethnicities and don't seem to discriminate among peoples (dwarfism, sickle-cell anemia, hemophilia, etc.) probably arose early on in human development, following branches of peoples as we diversified. Of course, with a disease like sickle-cell anemia, where having it can sometimes be a selective advantage (resistance to malaria), it makes sense that it would seem to be more prominent in people from malaria-infested regions. But these diseases still occur across great ethnicity lines.
ReplyDeleteHowever, with diseases like Tay-Sachs and Familial Dysautonomia, genetic diseases that are exclusive almost completely to a certain population, it is likely that these diseases arose after diversification of the human race. These diseases are seen in humans outside of their associated peoples, but this is likely due more to race interbreeding than to ancestral carriers outside of the carrying people.
ADDITION TO MY PREVIOUS POST (my last one was cut off):
ReplyDeleteIf you consider all genetic traits to be a "disease", of sorts, something that is passed down our anscestral lines, then the adaptations of the icefish to their cold environment can be compared to the arisal of genetic diseases. Developments like antifreeze and cold-adapted tubulins, traits that are present in all Antarctic notothenioid fish, are comparable to diseases like dwarfism and hemophilia; they developed early on, before differentiation of the larger category of Antarctic notothenioid fish. Traits that are specific to the icefish, such as loss of myoglobin in the muscles, would be like Tay-Sachs, developing after the split of the phylogenic line connecting all Antarctic notothenioid fish.
As Bersin already stated, it is apparent that certain diseases caused by gene mutations occurred at different points in the history of man. Ashkenazi Jews are known for having many genetic disorders that are uncommon or less common in other populations, such as Tay Sachs and Cystic Fibrosis. Such information leads to the conclusion that these genetic mutations only occurred after the Jewish population separated themselves from the rest of the human population by putting a social stigma on anyone who intermarries. Other diseases are common amongst all major human populations, which leads to the conclusion that the genetic mutations leading to those diseases occurred relatively early in the history of man, before there was great splits in the population. Other diseases, like sickle-cell anemia occur in multiple populations, in areas where malaria runs rampant. This means that at roughly the same time, the gene causing sickle-cell anemia mutated in multiple separate populations. From these examples, it is safe to conclude that not all diseases occur in certain populations due to relative time of the genetic mutations and locations of population groups at that time. Rather, some diseases occur at multiple locations at the same time. Getting back to the question, not all genetic diseases are caused in our hominid ancestors. Some are caused in our hominid ancestors, but others occur independently as conditions change to favor certain mutations over others.
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