October_16LecNotes-1 - October 16th 2007 Transcribed...

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October 16 th 2007 Transcribed lecture notes. (ppt) Routine class matters. Reading Chp 9 and 13. (ppt) We will finish discussing genetics. c Review history of the pioneering contributions made to genetics. c Try to imagine 150 years ago and how much we’ve learned about the nature of life since then. c Gregor Mendel—why would anyone have thought selective breeding would work? o He reached his conclusions based on observations (e.g. Domestication started 1,000’s of years ago). (ppt) Mendel’s Laws c See Figure 9.2 from your text and review the breeding experiment Mendel carried out [highlighted during class using this slide]. Note the incorporation of a ‘Control’. c P1 = parents c F1 = first generation offspring c F2 = second generation offspring (ppt) Mendel hypothesized there were alternative forms of genes [however, no one actually knew about genes or alleles at the time]. We now know these entities are called alleles (e.g. note the different expression (alleles) trait color). (ppt) See ppt for summary of what Mendel concluded c What does the Law of Segregation state? (see ppt) 1
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October 16 th 2007 Transcribed lecture notes. The Law of Segregation summarized: Mendel crossed a pure strain with green pods with a pure strain with yellow pods. All of the F1 generation was green ! (tending to disprove the blending theory – which states offspring are the result of a blending of the parents’ trait {imagine mixing yellow & green paint. Once mixed you can Never extract pure yellow color again. In contrast Mendelian genetics shows that traits are not blended they are an expression of an individual alleles). Was the yellow lost in Mendel’s experiment (thus blended)? To find out, Mendel Self crossed the F1 green plants resulting from a P1 mating of pure green with a pure yellow. Results indicated 3 out of every 4 offspring were green and 1 out of 4 was yellow. This 3:1 phenotypic ratio held for every trait he examined. Mendel concluded that the heritable factor (later called an allele for the given gene) for yellow was not lost, but was somehow masked by the green gene. He formulated a hypothesis with four parts: 1. There are alternative forms for genes (later called alleles ). 2. For each inherited characteristic, an organism has two alleles, one received from each parent. 3. A sperm or egg carries only one allele for each characteristic, because pairs are separated (or segregated) during the production of gametes (the process of meiosis). 4.
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This note was uploaded on 10/07/2009 for the course BIO G 109 at Cornell University (Engineering School).

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October_16LecNotes-1 - October 16th 2007 Transcribed...

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