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

2. Generalized Life Cycle
Fusion of haploid nuclei
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. Categories of Life Cycles
Haplontic
Haploid phase is predominant
Chlamydomonas Ulothrix
Diplohaplontic
Haploid and diploid phases are equally represented
Ulva
Diplontic
Diploid phase is predominant
Fern Echinoderm Ascaris Human
Animals

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

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

6. Haplontic Life Cycle of Ulothrix
Isogametes fuse to form diploid zygote
Gametangium: cell that produces gametes by mitosis
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
Haplontic Life Cycle of Ulothrix

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

8. Diplohaplontic Life Cycle
Diploid Sporophyte
Mitosis
Meiosis
Haploid Cells
in specialized structures
Diploid Phase
Zygote
Gametes
Fertilization/Syngamy
Mitosis
Haploid Gametophyte
Mitosis
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. Applying Your Knowledge
Diploid Phase
Haploid Phase
Both Diploid and Haploid Phases
Where is the sporophyte found?
Zoospores are part of which phase?
Where is the gametophyte found?
Where is the zygote found?

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

12. Diplontic Life Cycle of Fern
Archegonium: organ that produces eggs by mitosis
Plant
Smaller gametophyte
Larger, longer-lived sporophyte with tissues and organs
Spores produced by 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. Diplontic Life Cycle in Animals
Diploid Organism
Mitosis
Diploid Phase
in sex organs
Fertilization/Syngamy
Zygote
Gametes
Meiosis
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