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BIS 2B Lectures 10-12.2010.Outline

BIS 2B Lectures 10-12.2010.Outline - BIS 2B SPRING 2010...

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BIS 2B SPRING 2010 LECTURES 10 - 12 _____________________________________________________________________________ INHERITANCE _____________________________________________________________________________ I. D ARWIN S P ROBLEMS 1. Had there been enough time? a) We now know there’d been plenty of time (4.5 billion years, or so) b) Current evidence shows living organisms have been around for at least 3.5 billion years. 2. Where does variation come from? 3. How are traits inherited? 4. How do new species arise? a) We’ll come back to this, because Darwin also knew this was a problem. II. R EVIEW OF P RE -M ENDEL S OLUTIONS TO THE V ARIATION & H EREDITY P ROBLEMS 1. Pangenesis 2. Lamarckian inheritance 3. Blending inheritance III. M ENDEL & B EYOND 1. Heredity defined: The study of how the genetic composition of an individual GENOTYPE) and the environment influence its physical characteristics (PHENOTYPE) 2. The central questions: a) What are the mendelian laws of inheritance? b) What is the relationship between genes/particles and chromosomes? c) How do alleles (alternative states/variants of the same gene) interact? d) How do genes interact? e) What about traits that are controlled by multiple genes ( polygenic traits )? 3. Stuff we knew before Mendel: a) Sex & reproduction are linked b) Plant sex requires union of pollen & ovules c) Animal sex requires union of sperm & egg (1830) d) True-breeding lines, when mated, produce phenotypically uniform 1 st generation (F 1 ) offspring. 1) These offspring are often (but not always) intermediate between the two parental phenotypes. e) The F 2 generation often contains a mix of phenotypes, including the original parental types, plus the F 1 types. f) No one had ever actually analyzed the statistical distribution of phenotypes in F 1 ’s or F 2 ’s.
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BIS2B, Spring 2010 Lectures 10-12 - Page 2 4. A little bit about Gregor Mendel (1822-1884) 5. Why Mendel was smarter than everyone else: a) He asked the right question: you need to study organisms that actually interbreed. b) He knew he had to study traits that varied within species. c) He knew he had to use traits that varied discretely. d) He reasoned from Dalton’s atomic theory of chemistry (like Darwin reasoned from Lyell and Malthus). e) He knew he had to use organisms with high fertility so he could count frequencies of phenotypes. 6. Development of a theory of inheritance: it wasn’t easy! a) Mendel’s particulate theory in 1865 b) Weissmann proposes that hereditary particles reside on chromosomes in 1892 c) de Vries, Correns & von Seysennegg rediscover Mendl’s work in 1900 d) In 1902, Wilson et al . propose that meiosis is the reduction division (2N cells become 1N cells) that produces gametes. e) Johannsen distinguishes between genotype & phenotype in 1909. 1) genotype: an organism’s genetic composition 2) phenotype: an organism’s physical appearance, that reflects both its genetic make-up and the environment in which it develops and lives f) In 1915 Morgan admits that chromosomes carry genes.
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