Life Cycles

1. Life Cycles Observing Evolutionary Trends in the Life Cycles of Protists, Plants and Animals

2. Fusion of haploid nuclei Generalized Life Cycle Diploid Adult Mitosis Diploid Phase in specialized structures Diploid Cell Fertilization/Syngamy Meiosis Gametes Haploid Cells Haploid Phase Mitosis Mitosis Fusion of gametes Haploid Adult

3. Animals Categories of Life Cycles

4. Fertilization/Syngamy Diploid Cell Meiosis Isogametes Haploid Cells in poor conditions, cells of opposite mating type can fuse Mitosis Haplontic Life Cycle same size Diploid Phase Haploid Cells Haploid Phase

5. Resting spore withstands poor conditions Haplontic Life Cycle of Chlamydomonas • Photosynthetic protist showing an early eukaryotic life cycle • No mitosis in diploid phase

6. Isogametes fuse to form diploid zygote Gametangium: cell that produces gametes by mitosis Haplontic Life Cycle of Ulothrix • Photosynthetic Protist • No mitosis in diploid phase • Zygote produces spores by meiosis • Haploid gametophyte grows from spore by mitosis • Gametophyte can produce gametes or zoospores • Motile spores (zoospores) formed by mitosis or meiosis Sporangium: cell that produces spores by mitosis Spore: haploid cell that can grow by mitosis Gametophyte: multicellular haploid structure that produces gametes

7. For Ulothrix, spores are produced by Growth of a gametophyte occurs by For Chlamydomonas, spores are produced by For Ulothrix, gametes are produced by Mitosis Meiosis Both Mitosis and Meiosis Applying Your Knowledge

8. Mitosis in specialized structures Zygote Fertilization/Syngamy Meiosis Gametes Haploid Cells Mitosis Mitosis Haploid Gametophyte Diplohaplontic Life Cycle Diploid Sporophyte Diploid Phase Haploid Phase

9. Diplohaplontic Life Cycle of Ulva • Photosynthetic Protist • Introduction of Mitosis in Diploid phase • Gametophyte produces isogametes • Isomorphic gametophyte and sporophyte Sporophyte: multicellular diploid structure that produces spores by meiosis

10. Where is the sporophyte found? Zoospores are part of which phase? Where is the gametophyte found? Where is the zygote found? Diploid Phase Haploid Phase Both Diploid and Haploid Phases Applying Your Knowledge

11. Diploid Sporophyte Mitosis in specialized structures Zygote Meiosis Fertilization/Syngamy Haploid Cells Gametes Mitosis Haploid Gametophyte Mitosis Diplontic Life Cycle in Fern Diploid Phase Haploid Phase

12. Archegonium: organ that produces eggs by mitosis Diplontic Life Cycle of Fern • Plant • Smaller gametophyte • Larger, longer-lived sporophyte with tissues and organs • Spores producedby meiosis in sporangia on the underside of sporophyte leaves Antheridium: organ that produces sperm by mitosis contain sporangia(singular: sorus)

13. Sperm swim to archegonium and one sperm fertilizes the egg Archegonium: organ that produces eggs by mitosis Antheridium: organ that produces sperm by mitosis

14. Applying Your Knowledge • If a fern species has 5 pairs of homologous chromosomes, how many chromosomes would be found in a(n) • Sporophyte • Archegonium • Spore • Gametophyte • Sporangium (not including spores inside)

15. Diploid Organism Mitosis in sex organs Zygote Fertilization/Syngamy Meiosis Gametes Diplontic Life Cycle in Animals Diploid Phase Haploid Phase

16. Evolutionary Trends • Reduced length of haploid phase • Reduced amount of mitosis in haploid phase • Increased amount of mitosis in diploid phase • Increased size of diploid adult organism • Role of mitosis changes from reproduction in haploid phasegrowth in haploid phasegrowth in diploid phase • Single cells  Multicellular organisms • Increased tissue differentiation • Longer-lived species • Note that the role of meiosis and fertilization remains the same: to generate new combinations by sexual reproduction