14_Lecture_Post - Mendel and the Gene Idea What genetic principles account for the passing of traits from parents to offspring The blending

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Mendel and the Gene Idea What genetic principles account for the passing of traits from parents to offspring? The “blending” hypothesis is the idea that genetic material from the two parents blends together (like blue and yellow paint blend to make green) The “particulate” hypothesis is the idea that parents pass on discrete heritable units (genes) This hypothesis can explain the reappearance of traits after several generations Mendel documented a particulate mechanism through his experiments with garden peas
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Mendel used the scientific approach to identify two laws of inheritance Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments
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Mendel’s Experimental, Quantitative Approach Advantages of pea plants for genetic study There are many varieties with distinct heritable features, or characters (such as flower color); character variants (such as purple or white flowers) are called traits. Mating can be controlled Each flower has sperm-producing organs (stamens) and egg-producing organ (carpel) Cross-pollination (fertilization between different plants) involves dusting one plant with pollen from another
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Parental generation (P) Stamens Carpel First filial generation offspring (F 1 ) TECHNIQUE RESULTS 3 2 1 4 5 Mendel chose to track only those characters that occurred in two distinct alternative forms He also used varieties that were true- breeding (plants that produce offspring of the same variety when they self-pollinate)
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In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization The true-breeding parents are the P generation The hybrid offspring of the P generation are called the F 1 generation When F 1 individuals self-pollinate or cross- pollinate with other F 1 hybrids, the F 2 generation is produced
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The Law of Segregation When Mendel crossed contrasting, true-breeding white- and purple-flowered pea plants, all of the F 1 hybrids were purple When Mendel crossed the F 1 hybrids, many of the F 2 plants had purple flowers, but some had white Mendel discovered a ratio of about three to one (3:1), purple to white flowers, in the F 2 generation
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Figure 14.3-3 P Generation EXPERIMENT (true-breeding parents) F 1 Generation (hybrids) F 2 Generation Purple flowers White flowers All plants had purple flowers Self- or cross-pollination 705 purple- flowered plants 224 white flowered plants
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Mendel reasoned that only the purple flower factor was affecting flower color in the F 1 hybrids Mendel called the purple flower color a dominant trait and the white flower color a recessive trait The factor for white flowers was not diluted or destroyed because it reappeared in the F 2 generation
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Table 14.1 Mendel observed the same pattern of inheritance in six other pea plant characters, each represented by two traits What Mendel called a “heritable factor” is what we now call a gene
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This note was uploaded on 04/30/2011 for the course BIOL 1362 taught by Professor Loeblich during the Spring '08 term at University of Houston.

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14_Lecture_Post - Mendel and the Gene Idea What genetic principles account for the passing of traits from parents to offspring The blending

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