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Unformatted text preview: Lecture Topic: Darwin's logical difficulties Ideas of blending - false How does variation arise? Conducted systematic experiments on garden peas, 1856-1863 Was not recognized until after his death Focused on traits that have only 2 forms (discontinous traits) Green yellow seeds Smooth wrinkled seeds Continous traits - an infinite possibility of traits (skin tone) Cultivated true breeding lines and then studied results of crosses (green peas that only produced only green peas for generations) When two true breeding lines were crossed, 100% were yellow, after a second genetion 75% were yellow, 25% were green Gregor Mendel (1822-1884) monk Different variants of the same genes (alleles) Postulate #1: Hereditary characteristics are controlled by particulate unit factors (genes) that exist in pairs in individual organisms Postulate # 2: When there are two variations of particles and only one is expressed it is dominant and the other is recessive Genes for particular trait occur at particular site on chromosome (locus) Loci are lined up like beads on string Variants of genes at a single locus = alleles If alleles are the same = Homozygous...
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- Spring '07