Chapter 14 lecture - Chapter 14: Mendel and gene idea 1....

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Chapter 14: Mendel and gene idea 1. Mendel’s experiment Monohybrid cross: Mendel’s first law of segregation Dihybrid cross: Mendel’s second law of independent assortment Genetic terms 2.Crosses and Punnett square practices Human genetics 3. Extension on Mendelian genetics Examples
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Before the discovery of chromosomes: 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).
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Mendel documented a particulate mechanism through his experiments with garden peas.
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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 of plants can be controlled. Each pea plant has sperm-producing organs (stamens) and egg-producing organs (carpels).
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Stamens Carpel Parental generation (P) TECHNIQUE 1 2 3 4 Cross-pollination (fertilization between different plants) can be achieved by dusting one plant with pollen from another.
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Ingenuity of Mendel’s experiments Mendel chose to track only those characters that varied in an either-or manner. He also used varieties that were true- breeding (plants that produce offspring of the same variety when they self-pollinate). Pure breed, in-breeding the same predictable traits
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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, the F 2 generation is produced.
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TECHNIQUE RESULTS Parental generation (P) Stamens Carpel 1 2 3 4 First filial gener- ation offspring (F 1 ) 5 The blending hypothesis Predicts that all flowers in F1 generation to be light purple. The “particulate” hypothesis Predicts that the traits are unchanged (purple stays purple, white stays white).
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EXPERIMENT P Generation (true-breeding parents) Purple flowers White flowers F 1 Generation (hybrids) All plants had purple flowers F 2 Generation 705 purple-flowered plants 224 white-flowered plants A heritable factor: Purple color White color Color of the flower A gene: Allele (purple) Allele (white) A character
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P Generation Appearance: Genetic makeup: Gametes: Purple flowers White flowers PP P pp p F 1 Generation Gametes: Genetic makeup: Appearance: Purple flowers Pp P p 1 / 2 1 / 2 F 2 Generation Sperm Eggs P P PP Pp p p Pp pp 3 1 Phenotype Genotype Alleles Dominant allele: Capital letter P Recessive allele: Lower case letter p A Punnett square Genotype: 1:2:1 Phenotype: 3:1
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A Punnett square The possible combinations of sperm and egg can be shown using a Punnett square , a diagram for predicting the results of a genetic cross between
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This note was uploaded on 07/22/2011 for the course CHEM 1307 taught by Professor Staff during the Fall '10 term at University of Houston - Downtown.

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Chapter 14 lecture - Chapter 14: Mendel and gene idea 1....

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