Chapter 14 - Chapter 14 Mendel and the Gene Idea...

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Chapter 14 Mendel and the Gene Idea
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Preformationism – an pre-Mendel hypothesis of heredity Claimed either the egg or the sperm (exactly which was a contentious issue) contained a complete preformed individual called a homunculus. Development was therefore a matter of enlarging the homunculus into a fully formed being.
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Preformationism – Genetic diseases Was variously interpreted, examples: A manifestation of the wrath of God The mischief of demons and devils As evidence of either an excess of or a deficit of the father's “seed” As the result of “wicked thoughts” on the part of the mother during pregnancy
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Overview: Drawing from the Deck of Genes What genetic principles account for the transmission of traits from parents to offspring? Understanding the mathematics of probability was important in Mendel’s discoveries
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Hypotheses for heredity “Blending” hypothesis The idea that genetic material contributed by two parents mixes in a manner analogous to the way blue and yellow paints blend to make green “Particulate” hypothesis of inheritance: the gene idea Parents pass on discrete heritable units, genes
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Figure 14.1 Gregor Mendel Grew up in a part of Austria which is now the Czech Republic Documented a particulate mechanism of inheritance through his experiments with garden peas Failed his teacher exams But was trained in math & botany & research
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Concept 14.1: 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 Used quantitative methods Mendel chose to work with peas Because they are available in many varieties Because he could strictly control which plants mated
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Stamens Carpel Parental generation (P) TECHNIQUE 1 2 3 4 Crossing pea plants
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First filial gener- ation offspring (F 1 ) RESULTS 5 First generation All purple
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Some genetic vocabulary Character : a heritable feature, such as flower color Trait : a variant of a character, such as purple or white flowers* True-breeding : produce offspring of the same variety when they self-pollinate Hybridization : the mating or crossing of two true-breeding plants
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Research decisions Mendel chose to research Only those characters that varied in an “either-or” manner Mendel also made sure that He started his experiments with varieties that were “true-breeding”
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Research design In a typical breeding experiment Mendel mated two contrasting, true-breeding varieties, a process called hybridization The true-breeding parents Are called a P generation The hybrid offspring of the P generation Are called an F 1 generation When F 1 individuals self-pollinate An 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 offspring were purple When Mendel crossed the F 1 plants Many of the plants had purple flowers, but some had white flowers
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