Lecture12_Endosymbiosis

Lecture12_Endosymbiosis - BIS2C Lecture 12 • Eukaryotic...

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Unformatted text preview: BIS2C Lecture 12 Jan 30, 2012 • Eukaryotic life cycles alternation of generations haplontic diplontic • Review: eukaryotic cells • Mitochondria Endosymbiosis Origin • Chloroplasts Endosymbiosis Origin secondary and tertiary events Sexual reproduction • Is the formation of new individuals by the fusion of two haploid nuclei Sexual reproduction • All eukaryotic sexual life cycles have at least 2 steps: meiosis to reduce diploid cells to halpoids fusion of haploid gametes to produce a diploid cell Sexual reproduction • All eukaryotic sexual life cycles have at least 2 steps: meiosis to reduce diploid cells to halpoids fusion of haploid gametes to produce a diploid cell For multicellular organisms is the diploid or haploid phase multicellular? Sexual reproduction • All eukaryotic sexual life cycles have at least 2 steps: meiosis to reduce diploid cells to halpoids fusion of haploid gametes to produce a diploid cell For multicellular organisms is the diploid or haploid phase multicellular? Either, or both 3 Life cycle variations • Alternation of generations expansion of haploid and diploid phase through mitosis • Alternation of generations A diploid spore-forming organism gives rise to a haploid gamete-forming organism When haploid gametes fuse a diploid individual is formed. Both stages multicellular and undergo mitosis Ulva Isomorphic alternation of generations 3 Life cycle variations • Alternation of generations expansion of haploid and diploid phase through mitosis • Haplontic life cycle expansion of haploid phase The only diploid cell is the zygote generated through fertilization Haplontic life cycle Fungus ( Rhizopus oligosporus ) (Haploid organism) In the haplontic life cycle , the organism is haploid and the zygote is the only diploid stage. HAPLOID ( n ) Mature organism ( n ) DIPLOID (2 n ) Zygote (2 n ) Spores ( n ) Gametes Male (n) Female ( n ) 3 Life cycle variations • Alternation of generations expansion of haploid and diploid phase through mitosis • Haplontic life cycle expansion of haploid phase only The only diploid cell is the zygote generated through fertilization • Diplontic life cycle expansion of diploid phase only the only haploid cells are the gametes Diplontic life cycle Elephant ( Elephas maximus ) (Diploid organism) Zygote (2 n ) HAPLOID ( n ) Gametes Male ( n ) Female ( n ) In the diplontic life cycle , the organism is diploid and the gametes are the only haploid stage. DIPLOID (2 n ) Mature organism (2 n ) Clicker question Considering all the three types of life cycles shown: 1. Gametes undergo mitosis in the haplontic life cycle 2. Gametes never undergo mitosis or meiosis 3. Gametes undergo meiosis in the diplontic life cycle 4. Gametes undergo mitosis in the alternation of generations life cycle...
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Lecture12_Endosymbiosis - BIS2C Lecture 12 • Eukaryotic...

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