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Group 7. Heritability “The Nads” Jane Caldwell Jonathan Cumming Michelle Momany Rob Reenan Katrina Stewart Kathrin Stanger-Hall Kathy Takayama The Teachable Unit: Genetic Basis of Continuous Traits Learning Goals and Intended Outcomes: • Compare and contrast patterns of inheritance for traits exhibiting dominant-recessive and incomplete dominance behaviors. • Given a frequency distribution of traits in a population, predict the genotypes, and vice versa. • Explain the genetic basis for the normal distribution of a trait in a population. The Scaffold: In Previous Lectures… Previous Lecture: • Students will have mastered the basics of genes – Chromosomes, DNA – Gene replication • Students will have been exposed to the concepts of heredity – Simple Mendelian inheritance – Dominant-recessive behavior Previous Homework: • Develop an analogy or representation to explain simple inheritance. Include the terms below: – Gene, dominant & recessive alleles, genotype, phenotype • Groups shared this with another group at the beginning of the current lecture for engagement. Revisit: Mendel’s Peas • Certain traits exhibited specific patterns described by dominant/recessive behavior – Two phenotypes – Set population ratios • Such behavior is also evident in humans Simple Mendelian Traits Exercise - “Pair-Ear-Share” • Based on the distribution of traits in a population, scientists can make inferences about the genetics of inheritance in humans • Pair-Ear-Share • My ear lobe is: – A-Detached – B-Attached Detached Attached Clicker data collection Single Gene Incomplete Dominance • Systems often exhibit discrete yet complex phenotypic patterns – Four O’Clocks – Flowers have simple patterns of inheritance • No clear dominance • Incomplete dominance http://library.thinkquest.org/20465/genes.html Population Variation Continuous Traits • Phenotype frequency patterns often do not match those we have investigated, e.g., pea seed shape, earlobe attachment – Continuous variation in trait - cholesterol – Normal distribution in frequency Class Survey of a Continuous Trait: How Tall Are You? • • • • • A B C D E 5’ or shorter 5’1” – 5’4” 5’5” – 5’8” 5’9” – 6’ 6’1” or taller Clicker data collection Hypotheses for Continuous Variation Group Discussion and Hypothesis Development • Group discussion - 2 minutes • Generate a hypothesis to explain this height distribution Hypotheses for Normal Trait Variation • Incomplete dominance • Multiple genes • Environment The Mating Game: Multiple Gene-Incomplete Dominance Activity • Using coins and a cup, we will generate distributions of “coinotypes” that will be analogous to genotypes in a population • The penny is one gene – Alleles P (heads) and p (tails) • The nickel is another gene – Alleles N (heads) and n (tails) • These two “genes” control the same trait • Tossing a penny and a nickel together will generate the genotype of your gamete • Score your tosses with your “mate” The Mating Game: Multiple Gene Incomplete Dominance Activity • Roll twice, each “parent” record one offspring genotype • Scoring the genotypes of your offspring: A = 0 heads B = 1 head C = 2 heads D = 3 heads E = 4 heads Clicker data collection Mating Game: Debrief and Assumptions • Does the curve approach normality? • How many categories? • If you had another contributing gene, how would the categories change? • What constraints has the analogous system of coins placed on our genotypes? Traits and Distributions – Discrete phenotypes – Discrete distributions • Single gene, incomplete dominance – Discrete phenotypes – Discrete distributions Trait Frequency • Single gene, dominance Frequency Summary • Multiple genes, incomplete dominance – Continuous phenotypic traits – Continuous (normal) distributions Frequency Trait Trait Why Should We Care? • Most human traits are multigenic • For diseases, treatments are not simple – Multiple genes – Multiple targets for treatment • For next week, organize your group and identify a human disease that involves multiple genes – Google: polygenic disease – Select one and develop a 2 minute presentation for another class group Unit: Genetic Basis of Continuous Traits Basic concepts of heredity Scaffold (previous activities): • Active learning assignment • Lectures Review of background: Active learning exercise: “Pair-Ear-Share” Single gene incomplete dominance example Representation of traits in a population & Genetic basis of normal distribution Continuous traits: • Active learning exercise: Height • Students generate hypothesis Mating game: • Active learning exercise: Coins • Generation of data • Analysis of data • Extension to more complex situations transition Thanks to Lianna & the Summer Institute GO-NADS!!