Chapter 14

Chapter 14 - Chapter 14 - MENDEL AND THE GENE...

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Chapter 14 -- MENDEL AND THE GENE IDEA---Heredity: The Story of Gregor Mendel - 14.1.1 I. The father of genetics: Johann (Gregor) Mendel Mendel was a monk who was trained in science at the University of Vienna. Luck b/c - Monk – travel more - educated more – more time The realization that both parents contributed to the characteristics of the offspring preceded the work of Mendel. The favored explanation of how this occurred was the blending theory of heredity (an offspring got its traits by taking traits from both parents and blending them together) [the problem was that once the traits got blended together, they won’t separate again so the offspring will look the same but grandpa has red hair, son doesn’t have red hair, grandson has red hair] Modern genetics began with Mendel, and lead to the replacement of the blending theory with the particulate theory of heredity A. Among Mendel’s teachers were: Was trained 1. A physicist named Doppler who taught Mendel to use a quantitative experimental approach in studying natural phenomena. 2. A botanist named Unger who interested Mendel in the inheritable variation in plants Learned about plant reproduction B. These influences helped lead Mendel to the study of the variation of garden peas. Why peas? 1. Many different characters and traits (can get a lot of assistance) 2. Easy to grow 3. Grow a lot in a small space C. Characters – are detectable inheritable features of an organism (ex: eye, hair colors) D. Traits – variants of an inheritable character (hair color = brown) E. For Mendel’s pea plants the characters and traits he examined were (see table 14.1) 1. Flower color (purple or white) 2. Flower position (axial or terminal) 3. Seed color (yellow or green) 4. Seed shape (round or wrinkled) 5. Pod shape (inflated or constricted) 6. Pod color (green or yellow) 7. Stem length (tall or dwarf) Needs a lot of plants Mendel’s Findings: A First Look at Phenotypic Ratios - 14.1.2 I. Mendel started his experiments with true-breeding plant varieties which he hybridized (cross-pollinated) (see fig. 14.2) a. He controls the reproduction A. True-breeding – varieties in which self-fertilization leads to offspring that are the same type as parent a. Not mixing genes from 2 different parents b. From one parent but still mixing B. Takes pollen from one plant and put it into another B. Terminology for breeding (or genetics) experiments (see fig. 14.3) 1. P generation – winkled x smooth seed 2. F1 generation – 100% smooth 3. F2 generation – ¾ smooth Mendel’s Conclusion: Alternate Alleles and Dominance - 14.1.3 I. Mendel observed the transmission of the selected traits over these three generations and arrived at two principles of heredity: A. The law of segregation B. The law of independent assortment II. According to the law of segregation, two alleles for a character are packaged into separate gametes. A. Alleles (see fig. 14.4) – alternative forms of a gene that occupy a specific position (locus) on a specific chromosome
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This note was uploaded on 03/18/2010 for the course BIOL 1201 taught by Professor Wishtichusen during the Spring '07 term at LSU.

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Chapter 14 - Chapter 14 - MENDEL AND THE GENE...

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