352SLecture03_S11 - Genetics and Evolution: Lecture #3...

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1 Genetics and Evolution: Lecture #3 Today’s Topics 1. Gregor Mendel 2. Monohybrid cross: P, F1, F2 and F3 generations 3. Punnett square 4. Probability theory 5. Backcross and testcross Readings: Pierce, pgs. 43 - 54 Johann Gregor Mendel (1822 - 1884) Born in Czech Republic Augustinian monk Abbey in Brno Pea experiments (1856 – 1863) “Re-discovery” of work in 1900 “Father of modern genetics The Garden Pea ( Pisum sativum ) Advantages as an experimental organism: - Short generation time - Many genetically “pure” varieties - Produce large numbers of offspring - Crosses can be controlled by the experimenter Figure 3.1
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2 Mendel’s Approach Mendel made some good decisions: - Categorical traits with 2 distinct forms - Experimental using selective breeding - Detailed records - Formulated and tested hypotheses - Used mathematics Figure 3.1 Mendel’s First Experiments First experiments produced: - Law of Segregation (Mendel’s 1 st Law) - Concept of Dominance First Step: Testing for “true breeding” lines Next Step: The Monohybrid Cross - True breeding varieties for seed shape (round, wrinkled) - The P (“parental”) generation - Crossed to get a F1 (“±lial 1”) generation ! Figure 3.3
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3 Mendel’s First Experiments The F1 generation - All individuals displayed round phenotype - No sign of blending inheritance - F1’s are the monohybrids ! F2 obtained by “sel±ng” the F1 F2 phenotypes: Wrinkled phenotype reappears 5,474 round to 1,850 wrinkled (~3:1) Figure 3.3 Mendel’s First Experiments Experiment repeated for 6 other traits: - F1 all look like one of the P generation lines - Ratio of P generation traits always 3:1 in F1 Mendel makes some important conclusions! Conclusion I
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This note was uploaded on 05/07/2011 for the course BIOLOGY 352 taught by Professor Townsend during the Spring '08 term at San Diego State.

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352SLecture03_S11 - Genetics and Evolution: Lecture #3...

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