On pages 20 and 21, Dr. Moalem
considers the evolution of Cystic Fibrosis and confirms how it relates to big
ideas number 1 and 3 (the process of evolution drives the diversity and unity of life, and living systems store, retrieve, transmit, and respond to information essential to life processes).
Explain the functions of the gene CFTR and how it has to do with Cystic Fibrosis.
In addition answer why the disease became prevalent in Europe over the
17th-20th century. Are there any advantages to having the disease? (How is the
disease directly correlated to evolution?) What are the symptoms? Can you relate the type of mutation or the inheritance pattern of Cystic Fibrosis to any of the other diseases learned about at the Sam Rhine presentation or in class (Huntington's, etc)? Use scientific terms learned in class.
(Posted by Madeline Merageas, mmerage4@students.d125.org)
Cystic Fibrosis is a disease that affects the salt balance in blood cells, thus affecting the lungs, liver, pancreas, and intestines. Eventually, the mucus build-up causes disability and organ failure. Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) creates sweat, mucus, and digestive juices for the body; once this gene is affected, unregulated amounts of mucus, sweat, and digestive juices are made causing problems and future organ function. Some of the symptoms of Cystic Fibrosis include: skin that tastes very salty, constant coughing often with phlegm or extra mucus, frequent lung infections(such as pneumonia and bronchitis), shortness of breath, little weight gain and poor growth.
ReplyDeleteBetween 1600s and 1900s in Europe, Tuberculosis was greatly affecting the population and causing “20 percent of all the deaths in Europe” (21). People that were carriers of the Cystic Fibrosis gene were provided with a prevention towards tuberculosis; they were able to survive and thus reproduce causing future generations to be more prone to having CT or being a carrier. The advantage to Cystic Fibrosis is being able to survive through the Tuberculosis onslaught. During that time, having one set of the Cystic Fibrosis gene was a favorable trait that allowed for carriers to prosper. Although, once Tuberculosis stopped being a threat, the European population was left with a highly unfavorable trait in its population that would lead to a major downfall. The advantage lies within natural selection. As in one instance, the pressure of environment caused CT to be favored, once the population evolved into CT carriers, the population is now faced with new pressures that will cause a new evolutionary pathway. It can be inferred that if the disease is a favorable trait it will be positively correlated with evolution as it drives the diversity and unity of life (Big Idea 1).
Cystic Fibrosis is an autosomal recessive gene that is inherited. In order to have the disease, the person must have “two copies of the mutated gene,” thus making the disease recessive (20). Parents that are carriers and not affected have a 1 in 4 chance that their child will have Cystic Fibrosis. The genotypic ratio for the parents would be 1:2:1 and the phenotypic ratio would result in 3:1. Similarly, Huntington’s disease is also inherited yet is a dominant gene. This means that if one parent has Huntington’s disease, the probability of offspring having the disease is either 50% or 100% depending on the genotype. Although Huntington’s disease is dominant, it could be less common than Cystic Fibrosis in certain populations because of the process of evolution and environmental pressures that were mentioned above.
http://www.medicalnewstoday.com/articles/147960.php
Sigal Sasson (ssasson3@students.d125.org)
The function of the CFTR gene (or rather the protein synthesized from the gene) involves the forming of chloride channels in cell membranes, the washing away of bacteria/mucus in the lungs, the washing away of pathogens in the intestines, and the recycling of salt out of sweat glands and back into the skin. The information from the gene that contains instructions to perform these functions relates to Big Idea 3: living systems store, retrieve, transmit, and respond to information essential to life processes. A person with a mutated CFTR gene will have thick mucus that blocks these channels, inhibiting his/her body from performing these functions.
ReplyDeleteThis relates to Tte symptoms of Cystic Fibrosis which are very widespread as the disease affects the respiratory, digestive, and reproductive systems of the affected individual. For instance, some symptoms of Cystic Fibrosis may be lung infections, sinusitis, mucus buildup in airways and/or pancreas, infertility (for males because born without vas deferens), or mucus blockage in the cervix making it difficult for women to get pregnant. In general, however, these symptoms all stem from a lack of enzymes to absorb fats and protein, causing a insufficient nutrients which cases poor weight gain and growth.
The CFTR gene that causes Cystic Fibrosis involves a deletion of three base pairs. This causes a deformed protein to be synthesized and is marked as defective, thus never reaching the cell membrane. Additionally, this gene is homozygous recessive as stated on page 20 of Survival of the Fittest, which means that two copies of the mutated gene are needed to cause the disease; however, many people are carriers of the gene, having only one copy. As Sigal Sasson stated, since Cystic Fibrosis is autosomal recessive, there is a 1 in 4 chance that an offspring would have Cystic Fibrosis if born to two carrier parents. Werner Syndrome, mentioned in Sam Rhine’s presentation, possesses the same inheritance pattern as it is also homozygous recessive. The inheritance pattern of the CFTR gene actually explains to an extent why Cystic Fibrosis became prevalent in Europe over the 17th-20th century. According to Dr. Moalem, since so many people carried a copy of the gene, they had some protection for tuberculosis which caused 20 percent of all deaths during that time period. This protection from tuberculosis is an advantage to having Cystic Fibrosis from an evolutionary standpoint, and explains why Cystic Fibrosis may have been so prevalent in Europe over the 17th-20th century. The genetic mutations that eventually led to disease prevention relates to Big Idea 1: the process of evolution drives the diversity and unity of life. Now, when a vaccine for tuberculosis exists (depleting the advantage of having Cystic Fibrosis), the Cystic Fibrosis occurrence has not coincidentally gone down as well.
In addition to causing protection against tuberculosis, the mutation in the CFTR gene has three other evolutionary advantages. According to a 1967 study published in American Journal of Human Genetics, Cystic Fibrosis heterozygotes were associated with successful childbirth (more so than a control group of people with normal CFTR genes). A carrier of a mutant CFTR gene also has protection against cholera and typhoid fever due to nonfunctional chlorine channels.
http://serendip.brynmawr.edu/biology/b103/f02/web1/emyers.html
http://www.nhlbi.nih.gov/health/health-topics/topics/cf/signs.html
Stephanie Li (steli4@students.d125.org)