On pages 8-9, Dr Moalem discusses the Bubonic Plague and how somewhere between “one-third and one-half of the population was killed.” He later goes on to explain how even though that the Bubonic Plague was a “gruesome disease,” it didn’t kill everyone it affected. Lymphatically speaking, the survival rate was “one in three.” When it’s airborne, on the other hand, the disease kills “nine out of ten.” Dr Moalem later went on to describe how our ancestors who had hemochromatosis also had an advantage if they were battling the Bubonic Plague. Given that this was an advantage, and that over 25 million people died from the Bubonic Plague, shouldn’t Hemochromatosis be a prevalent genetic mutation in our current populations given that it is dominant? Well it was, and Dr Moalem did explain how Hemochromatosis was prevalent in the surviving generation, and some generations after that. However, Hemochromatosis is currently only in every one out of a hundred people.
Relating to Big Idea #1 (The process of evolution drives the diversity and unity of life), we know how Hemochromatosis is no longer as prevalent in the gene pool than it was 700 years ago (if you don’t, look at Lindsay Pontello’s question). This time, to prove it, use the recent chapter we studied of “Meiosis and Patterns of Inheritance.” Using what you’ve learnt, describe how Hemochromatosis has been passed down through generations, especially since the Bubonic Plague. Describe whether Hemochromatosis is autosomal recessive, autosomal dominant, etc, and provide several facts as to why this is. Explain how diseases such as the deadly Bubonic Plague haven’t come back, and how the Bubonic Plague was able to go away of years of killing people. Describe which ethnicities have Hemochromatosis, and compare that to patterns of inheritance. Finally, describe how a deadly genetic disease, such as Hemochromatosis, can be beneficial in relation to modern science; how can something harmful provide a benefit in a world of antibiotics and other medicines?
Noella James (noellajames@gmail.com)
Relating to Big Idea #1 (The process of evolution drives the diversity and unity of life), we know how Hemochromatosis is no longer as prevalent in the gene pool than it was 700 years ago (if you don’t, look at Lindsay Pontello’s question). This time, to prove it, use the recent chapter we studied of “Meiosis and Patterns of Inheritance.” Using what you’ve learnt, describe how Hemochromatosis has been passed down through generations, especially since the Bubonic Plague. Describe whether Hemochromatosis is autosomal recessive, autosomal dominant, etc, and provide several facts as to why this is. Explain how diseases such as the deadly Bubonic Plague haven’t come back, and how the Bubonic Plague was able to go away of years of killing people. Describe which ethnicities have Hemochromatosis, and compare that to patterns of inheritance. Finally, describe how a deadly genetic disease, such as Hemochromatosis, can be beneficial in relation to modern science; how can something harmful provide a benefit in a world of antibiotics and other medicines?
Noella James (noellajames@gmail.com)
Hemochromatosis stayed around back then because "though it will kill them decades later, [people with hemochromatosis] are much more likely than people without hemochromatosis to survive the plague, reproduce, and pass the mutation on to their children" (15). The explanation of why now it is in only one out of every hundred people is that current generations no longer have the major threat of plague, such as the bubonic plague, that affected past generations. The compromise in the past was that the negative consequences of iron buildup in the body would be far outweighed by the protection against the bubonic plague, which killed around 80 percent of people who were infected and left untreated. However, in our times, there is nothing to offset the negative effects of hemochromatosis. Therefore, it is selected against in populations, leading to a reduced frequency of the allele in populations over generations. This relates to Big Idea 1 (The process of evolution drives the diversity and unity of life) since we can see exactly how environmental factors have caused different variations in human populations over time. Back then, when bubonic plague was the prevailing threat, the frequency of hemochromatosis was at its highest. Now, when protection against deadly diseases is no longer important, especially considering the availability and effectiveness of modern medicine, hemochromatosis is on the decline in populations.
ReplyDeleteBubonic plague is still around today, albeit at a much more manageable level. According to the World Health Organization, there are about 1,000 to 3,000 cases of the bubonic plague in the world each year and 10-15 cases in the United States according to the CDC. The biggest reason for the massive decrease in numbers is the removal of the method for the bubonic plague to spread. Previously, the spread of the bubonic plague was greatly aided by fleas and flea-infested rats, which would travel aboard ships to distant locations. This method has been minimized greatly in modern society. In fact, places with the highest risk are rural and urban areas of developing countries, where conditions are less sanitary. Another reason for the decrease, as mentioned above, is the rise of modern medicine. Antibiotics such as streptomycin or tetracyclin are given and symptoms are treated. This also helps greatly reduce the mortality rate.
Regarding our Meiosis and Inheritance unit, hereditary hemochromatosis is autosomal recessive. According to kidhealth.org, one in every 8 to 10 people carry one copy, or allele, of the hemochromatosis defective gene. The reason why 1 out of every 8-10 people can have it but only 1 out of every 100-200 people are affected is because of hemochromatosis being an autosomal recessive disease. The majority of people are carriers, meaning they have one normal allele of the gene and one mutant copy of the gene. Only when someone has 2 copies of the defective gene do the symptoms of hemochromatosis appear. When two carriers have a child, that child only has a quarter of chance of getting both defective alleles based on a Punnett Square (1/2 * 1/2).
In terms of gene expression, the reason why hemochromatosis is autosomal recessive deals with its protein product. People with hemochromatosis have excess iron in their body due to the mutated protein associated with hemochromatosis. This protein is involved in the chelating of iron, which occurs when the body essentially locks up iron using special iron chelator proteins. According to sickle.bwh.harvard.edu, chelators bind tightly to metal ions, which make these metal ions chemically inert. One complex protein chelator that biological organisms produce is transferrin. Another function of chelators, as Dr. Moalem mentions, is to limit "the ability to access iron within our macrophages," which is "what makes some intracellular infections deadly and others benign" (13). From a protein database on the National Center for Biotechnology Information website, "The protein encoded by this gene is a membrane protein that is similar to MHC class I-type proteins [from our past unit!] and associates with beta2-microglobulin (beta2M). It is thought that this protein functions to regulate iron absorption by regulating the interaction of the transferrin receptor with transferrin." Having one mutant allele for hemochromatosis causes a person's body to produce one "dose" of the normal protein and one "dose" of the mutant protein. For this protein, just one dose of a normal protein is able to balance out the effects of the mutant protein so that a person doesn't experience the harmful symptoms, which is why two mutant alleles are needed, making hemochromatosis autosomal recessive.
ReplyDeleteAccording to the American Hemochromatosis Society, ethnic groups that are most affected are Anglo-Saxons. Specifically, "those with an Irish/Scottish/Celtic/British heritage have an even higher prevalence of the HH [hemochromatosis] mutation." Hispanics and African Americans have a higher prevalence of hemochromatosis as well.
Sources:
http://kidshealth.org/parent/general/aches/hh.html
en.wikipedia.org/wiki/Black_Death
http://www.cdc.gov/Features/Hemochromatosis/
http://sickle.bwh.harvard.edu/chelators.html
http://rarediseases.about.com/cs/bubonicplague/a/111602.htm
http://www.americanhs.org/faq.htm
http://www.ncbi.nlm.nih.gov/gene?Db=gene&Cmd=ShowDetailView&TermToSearch=3077
Austin Hua (auhua4@students.d125.org)