6 - from genotype to phenotype

6 - from genotype to phenotype - BIOLOGY 325H From Genotype...

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BIOLOGY 325H From Genotype to Phenotype 1/28/08 A central component of evolution is that natural selection acts at the level of phenotypes - i.e. the survival and/or reproduction of certain phenotypes are favored - whereas evolution occurs through changes in the genetic structure of a population. Thus, the way in which genotype is expressed as phenotype can both limit and shape the process of evolution. In this lecture we will focus on how the genotype-to-phenotype transformation influences evolution by natural selection. First, we will consider variations in allelic dominance. Second, we will leave the highly simplistic model of 'one gene ! one trait' and consider the much more realistic situation in which (i) a single gene governs multiple traits or (ii) a single trait is controlled by multiple genes. Third, we will consider situations in which a heritable trait is modified by environmental factors or gender. Learning goals 1. Assuming similar selection coefficients, will a dominant allele or a recessive allele be eliminated more rapidly by natural selection? Can natural selection remove a recessive allele from a large breeding population? What other factor can interact with natural selection to bring about the elimination of a purely recessive allele? 2. What is incomplete dominance? How does incomplete dominance affect the ratio of phenotypes produced by a monohybrid cross in which both parents are heterozygotes? 3. Learn the genetics of the MN and ABO blood groups in humans. What does it mean to say that the I A and I B alleles are codominant? How is codominance distinguished from incomplete dominance? 4. What is the difference between pleiotropy and a multilocus trait? Can a single gene be pleiotropic and also affect a multilocus trait? 5. What are penetrance and expressivity? What is a temperature-sensitive allele, and why is it called 'conditional'? How does temperature sensitivity of melanin production account for the light and dark markings in the fur of a Siamese cat? 6. Learn the genetics underlying the inheritance of male pattern baldness in humans. Why is this pattern of inheritance said to be "sex-influenced"? How is that different from "sex- limited inheritance"? _________________________________________________________________________ Practice your knowledge by solving the following problems from Klug: 4-6 4-7 4-14 4-23 4-25 4-33
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1 Over the course of many generations, a breeding population or species will display a series of changes called an evolutionary trajectory . This trajectory is shaped by the
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6 - from genotype to phenotype - BIOLOGY 325H From Genotype...

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