Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Nutriepigenomics wikipedia , lookup
Gene expression programming wikipedia , lookup
Population genetics wikipedia , lookup
Gene expression profiling wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Genome (book) wikipedia , lookup
Designer baby wikipedia , lookup
Fetal origins hypothesis wikipedia , lookup
PTC Tasting and Evolution Why you don’t like to eat veggies and other bitter foods Why do we have taste preferences? • • • • Is it in our genes? If so why? Can it influence dietary preferences? How do I determine if data is valid? Vocabulary • SNPs – single nucleotide polymorphism or a single change in a gene that allows for differentiation in that gene (an A is changed to another nucleotide) • Locus – location on the chromosome • Haplotype - a group of alleles of different genes on a single chromosome that are closely enough linked to be inherited usually as a unit (Merriam-Webster Online Dictionary 2008) example: red hair and blue eyes are on the same chromosome and are inherited together. Who came up with the PTC paper test? • Fox, 1931 • Olsen et.al. (1989) data fitted best a 2-locus model in which one locus controls PTC tasting and the other locus controls a more general taste ability. • Are there differences in population ability to taste? • Who came up with the PTC paper test? • The incidence of inability to taste PTC is much lower in blacks than in whites in North America: 3% as compared with 30% PTC Factoids • It has long been proposed that a relationship of PTC nontasting to cretinism exists (e.g., Shepard, 1961). • PTC is structurally similar to 6-n-propylthiouracil (PROP) and the naturally occurring anti-thyroid substance l-goitrin; all members of this class of chemicals have anti-thyroidal activity and are not tasted by PTC non-tasters (Shepard, 1961). • This means that PTC non-tasters could develop thyroid problems because they cannot taste alkaloids as readily Why can I taste PTC? • There has been a suggestion that PTC tasting in humans is related to a component of saliva: Cohen and Ogdon (1949) claimed that PTC tasters can taste PTC only if it is dissolved in their own saliva • If the tongue is dried and then presented with PTC dissolved in someone else's saliva, it is tasteless. Jones and McLachlan (1991) described a technique for fitting mixture distributions to data on PTC sensitivity. How is PTC taste related to natural selection? • Tepper (1998) discussed the classic explanation for the persistence of the PROP polymorphism, i.e., a selective advantage for avoidance of harmful compounds in the environment that are often bitter tasting • PROP and PTC are chemically related to the isothiocyanates and goitrin, bitter-tasting compounds that are present in cruciferous vegetables such as cabbage, broccoli, brussel sprouts, turnips, and kale. How is PTC related to natural selection? • When eaten in large quantities, these compounds interfere with iodine metabolism, producing thyroid enlargement and goiter-like symptoms. Tepper (1998) noted that the incidence of thyroid deficiency disease is relatively rare among PTC tasters. Modern Society? • In modern society, however, avoidance of bitter-tasting foods may have health disadvantages, since epidemiologic studies indicate that diets low in fruits and vegetables and high in fat may be associated with increased risk of heart disease and cancer Possible effect on dietary preferences in modern times • Children carrying one or two bittersensitive regions of a gene prefer higher concentrations of sucrose solutions and have a stronger preference for sweettasting food and beverages than did the bitter-insensitive kids. (http://www.sciencedaily.com/videos/2005/ 0508-the_taste_gene.htm) • How could this affect obesity problems? Why aren’t PTC genes lost in a population • • • • If PP = homozygous PTC tasters If AP = PTC tasters who are heterozygous If AA = homozygous non tasters, then If AP mates with AP, what percent of their children will be – Tasters – Nontasters Genetics of PTC • Fisher et al. (1939) hypothesized that the pervasive phenotypic variation in PTC taste perception is due to balancing natural selection, which may have favored heterozygotes. • Wooding et. al (2004) analyzed the entire coding region of PTC (1,002 bp) in a sample of 330 chromosomes from different populations (62 African, 138 Asian, 110 European, and 20 North American) by use of statistical tests for natural selection that take into account the potentially confounding effects of human population growth. Alleles and PTC tasting • Two haplotypes of intermediate frequency corresponding to 'taster' and 'nontaster' phenotypes were found. • Supported the hypothesis of Fisher et al. (1939) and suggested that balancing natural selection has acted to maintain 'taster' and 'nontaster' alleles at the PTC locus SNPs and Phenotypes • Kim et al. (2003) cloned the TAS2R38 gene (607751) and identified 3 coding SNPs giving rise to 5 haplotypes worldwide that completely explain the bimodal distribution of PTC taste sensitivity (super taster vs. taster). • Distinct phenotypes were associated with specific haplotypes, which demonstrated that the TAS2R38 gene has a direct influence on PTC taste sensitivity and that sequence variants at different sites interact with each other within the encoded gene product. Hypothesis 1 If tested for the ability to taste PTC paper, there will be a greater number of tasters than non-tasters in a random section of the community population. Postulate: Tasting alkaloids allowed humans to detect the presence of poisonous substances. Hypothesis 2 If tested for the ability to taste PTC paper, there will be a greater number of tasters than non-tasters in the females tested in a given population. Postulate: Tasting alkaloids allowed women to detect the presence of poisonous substances in foods they gathered. Hypothesis 3 If tested for the ability to taste PTC paper, there will be a greater number of tasters than nontasters in the Caucasian vs. non-Caucasian members of the tested population. Postulate: Foods such as bitter melon, collard greens, kale and other bitter tasting foods are eaten by Caucasians who do not have the allele. Hypothesis 4 If tested for the ability to taste PTC paper, there will be a greater number of tasters than non-tasters in the non-Caucasian (blacks, Asians, Hispanic) members of the tested population. Postulate: Foods such as bitter melon, collard greens, kale and other bitter tasting foods are eaten more frequently by non-Caucasians. Groups • • • • • • • • Group 1 – Tyler, Steph, Hyeon Group 2 – Claire, Kelly, Michael Group 3 – Hallie, Sara Group 4 – Adam, Ryan Group 5 – Connor, Meghan, Morgan M Group 6 – Morgan L., Patrick, Group 7 – Josh, Rachel Group 8 – Chris, Jessie Jobs within groups 1. Researcher(s) – researching information from the questions 2. Data analyzer – runs T-test and creates histogram based on the hypothesis chosen 3. Everyone choses a part of the lab to write. What you will do 1. 2. 3. 4. 5. 6. 7. 8. Get into groups Collate data for the various subgroups (Caucasians, AfricanAmericans, Asian- Americans, Hispanic-Americans) Put data on the main data sheets on the computer; copies will be generated Have one person select a hypothesis for your group to prove or disprove based on the data Conduct an unpaired T-test on the data for your hypothesis Create a histogram or bar graph of your data for comparison Use the Analysis questions to help you in your discussion PTC lab.doc What you will hand in • Group PPT, with each person’s work clearly identified • Standard Lab PPT or Prezio – Introduction, with hypothesis – Method of Testing (explain how you conned people into tasting the papers) – Data Analysis, containing T-test results and histogram – Discussion, including validation or refutation of hypothesis and data to back up your claim, as well as inclusion of answers to research questions from handout – Conclusion, for your hypothesis