MendelandMendelism

MendelandMendelism - 10/27/11 Mendel: Darwin s Savior or...

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10/27/11 1 Mendel: Darwin ` s Savior or Opponent Gregor Mendel An Augustinian monk, Mendel studied physics and natural science in Vienna, but lived most of his adult life in the cloister at Altbrunn (now Brno in the Czech Republic) Starting in 1856 he conducted plant breeding experiments in the cloister ` s garden Seeking the l law governing the formation and development of hybrids z Mendel ` s Breeding Experiments An lucky choice of model organism. Chose to study peas because • They exhibit relatively easy to distinguish traints • They naturally self pollinated but are easy to cross-pollinate To characterize their behavior in crosses, Mendel introduced the vocabulary of dominant (traits that appeared in hybrid crosses) and recessive characters (one’s that only appeared in subsequent generations)
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10/27/11 2 Mendel ` s Procedure n Began by cross-pollinating between pure breeding lines with alternative traits—yellow/green, smooth/dented n Found that all members of the F1 generation exhibited the dominant traits n Allowed members of the F1 generation to self-pollinate, generating the F2 generation n And analyzed the numbers exhibiting the dominant and recessive traits Form of seed Round / Wrinkled 5474 1850 2.96:1 Color of albumin Yellow / Green 6022 2001 3.01:1 Color of seed coat Violet flowers / White flowers 705 224 3.15:1 Form of pods Inflated / Constricted 822 299 2.95:1 Color of unripe pods Green / yellow 428 152 2.81:1 Position of flowers Axial / terminal 651 207 3.14:1 Length of stem Long / short 787 277 2.84:1 F2 Generation Created from Hybrids F2 Generation n Produced by self-pollination of members of the F1 generation n When members of the F2 generation were allowed to self pollinate n Individuals with recessive traits bred pure n One out of three of those showing the dominant character produced only offspring with the dominant character n Theoretical problem for Mendel—what could explain these and other patterns Mendel found?
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10/27/11 3 Mendel ` s l Laws z n Three laws commonly attributed to Mendel: n Law of segregation n Only one of a pair of alternative traits will be passed on through a gamete n Law of independent assortment n Different traits are inherited independently from each other n Law of dominance n One trait will l dominate z over the other in hybrids Mendel ` s Hypothesis (in modern terms) Proposed that behind the characters lay factors Pollen and egg cells each possessed the factor for either the dominant or recessive trait What evidence does Mendel have for these factors? Only that they could account
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MendelandMendelism - 10/27/11 Mendel: Darwin s Savior or...

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