Review Session 8 Key

Review Session 8 Key - Sun Nov 20 review session for...

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1 Sun. Nov. 20 review session for BICD100 FA2011 with answers Topics: QTL mapping, heritability analysis in humans, complex traits, GWAS, evolutionary genetics 1. Consider the following table showing concordance (percent of cases where twins have same phenotype) between twins for various phenotypes in humans. Trait Concordance in monozygotic twins Concordance in dizygotic twins mental retardation 97 37 handedness 79 77 epilepsy 72 15 schizophrenia 69 10 diabetes 65 18 breast cancer 6 3 a. Which trait shown appears to be the most heritable and what is the evidence supporting that conclusion? Schizophrenia, which has the highest ratio of MZ:DZ concondance of all the traits shown here b. Which trait appears to be the least heritable and what is the evidence supporting that? Handedness, which has a nearly 1:1 ratio of MZ:DZ concordance c. What does the nearly equal, high concordance values for MZ and DZ twins in handedness suggest about the factors determining handedness? Concordance is very high but equally high in both MZ and DZ twins, suggesting that the concordance is due mainly to environmental factors. This suggests that parents, teachers, other children, etc. have a major influence on a child’s handedness! d. Name one thing which, if it occurred, would lead to an overestimate of heritability using this approach. If monozygotic twins are treated more similarly than dizygotic twins, that would account for some of the higher concordance value seen in MZ vs. DZ twins and lead to overestimation of heritability. If the study was not limited to same sex pairs of DZ twins, that could also account for some of the higher concordance value in MZ vs. DZ twins. 2. What is the difference between a complex trait and a quantitative trait? Quantitative trait: no discrete phenotypic categories but instead a continuum, typically controlled by multiple genes as well as by environment Complex trait: trait (which may be quantitative or all-or-none) whose genetic control is obscured by one or more confounding factors such as multigenic control, incomplete penetrance, more than one gene that can mutate to give same phenotype, trait may be “phenocopied” in a non-heritable way 3.
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Review Session 8 Key - Sun Nov 20 review session for...

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