BIOL211#16 - Chapter 16 Genetic traits are transmitted from...

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1 Chapter 16 Simple Patterns of Inheritance Genetic traits are transmitted from generation to generation (inheritance) Possible hypotheses – Blending hypothesis – Particulate hypothesis Blending hypothesis – Genetic material contributed by two parents mixes in a manner analogous to mixing two paint colors – Prevailing thought in the late 1700’s and 1800’s Particulate hypothesis – Parents pass on discrete heritable units (genes) that retain their separate identities in their offspring – First proposed by Gregor Mendel in the 1860’s Mendel’s Laws Mendel discovered the basic principles of heredity by mating (crossing) garden peas in hybridization experiments Why garden peas? – Available in many varieties with distinct characters and traits – Self-fertilizing – Ease of making crosses Figure 16.2
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2 Crossing pea plants Figure 16.4 Gregor Mendel 1822 - 1884 Mendel chose to track only those plants that differed in a single character – Produced a monohybrid cross Mendel also made sure that he started his experiments with varieties that were “true-breeding” Mendel cross-pollinated (hybridized) two contrasting, true-breeding varieties – True-breeding parents are the P generation – The hybrid offspring are the F 1 generation – When F 1 individuals self-pollinate, the F 2 generation is produced Figure 14.3 Mendel’s experiments allowed him to postulate the following: – Traits exist in two forms: dominant and recessive – Individuals carry two genes for a given character; the genes are variant forms called alleles – Alleles separate during gamete formation Dominant and recessive traits – Dominant describes the displayed trait – Recessive describes a trait that is masked by the presence of a dominant trait – Contradicted the prevailing notion of blending inheritance
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3 Genes and alleles – Mendel concluded that genetic determinants of traits are “unit factors” (genes) that are passed intact from generation to generation – Every individual carries two genes for a
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This note was uploaded on 10/02/2011 for the course BIOL 211 taught by Professor Boury during the Spring '08 term at Iowa State.

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BIOL211#16 - Chapter 16 Genetic traits are transmitted from...

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