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• Introduction to Development – Eukaryotic Gene Expression – Cellular Signaling • Simple Eukaryotic Development: Yeast – Model systems • Pattern formation; chick limbs • Organ identity; floral development Reading Cpt 21, pp. 406-410 Cpt 38, pp. 747-748 Cpt 35, pp. 682-683 Plant vs. Animal Development Responds to environment: opportunistic Body plan formed early: genetically determined Meristems Apical Shoot or root=primary growth and development Lateral Secondary growth= thickening Meristems Plant tissue that remains embryonic as long as the plant lives, allowing for indeterminate growth shoot meristem flower meristem leaves, stems flowers shoot meristem leaves, stems environmental trigger flower meristem flowers shoot meristem leaves, stems environmental trigger signaling molecule flower meristem flowers Shoot meristem Enviromental trigger Signaling molecules (plant hormone) Flower meristem 39.17 shoot meristem = Shoot meristem identity genes ON Flower meristem identity genes OFF shoot meristem flower meristem = Shoot meristem identity genes ON Flower meristem identity genes OFF = Shoot meristem identity genes OFF Flower meristem identity genes ON flower meristem identity genes organ identity genes Four types of flower organs Sepal Petal Stamen Carpel 30.6 Model organism to study flower organ development? Arabidopsis thaliana Common wall cress Four types of flower organs Sepal Petal Stamen Carpel 21.18A How identify these organ identity genes? How identify these organ identity genes? Look for mutant flowers Three families of genes affect flower organ identity Wildtype Gene A mutant Gene B mutant Gene C mutant 21.18C Question: How can the products of three genes produce four organs? Hypothesis: Genes active in specific regions of meristem Test: Where are Genes A, B C active? RNA from Gene A = red dye RNA from Gene B = yellow dye RNA from Gene C = orange dye 21.18B Conclusion: Hyposthesis supported: Genes active in specific regions of meristem What types of molecules are encoded by the organ identity genes? What types of molecules are encoded by the organ identity genes? Transcription factors Homeotic genes • Master regulatory genes • Transcription factors Homeotic genes • First identified in fruit flies Mutations = legs in place of antennae Homeotic genes First identified in fruit flies Mutations = legs in place of antennae Plants Mutations = sepals in place of petals Homeotic genes • Master regulatory genes • Transcription factors • Genes that control the overall body plan of an organism by controlling the developmental fate of groups of cells Organ identity Genes A, B and C are: Transcription factors Master regulatory genes Plant homeotic genes Bio 103 Home