Life CyclesLife Cycles

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

Generalized Life CycleGeneralized Life Cycle

Haploid Phase

Meiosis

Gametes

Fertilization/Syngamy

Haploid Cells

Haploid Adult

Diploid Adult

Mitosis

Fusion of gametes

Fusion of haploid nuclei

Diploid Phase

Mitosis

Mito

sis in specialized

structuresDiploid Cell

Categories of Life CyclesCategories of Life Cycles

HaplonticHaplontic Haploid phase Haploid phase is predominantis predominant

ChlamydomonasChlamydomonasUlothrixUlothrix

DiplohaplonticDiplohaplontic Haploid and Haploid and diploid phases diploid phases are equally are equally representedrepresented

UlvaUlva

DiplonticDiplontic Diploid phase is Diploid phase is predominantpredominant

FernFernEchinodermEchinodermAscarisAscarisHumanHuman A

nim

als

Ani

mal

s

Haplontic Life CycleHaplontic Life Cycle

Haploid Phase

Diploid Phase

Mei

osis

Haplo

id C

ells

Isogametes

Fertilization/Syngamy

Diploid Cell

Haploid CellsMito

sis

in poor conditions, cells of opposite mating type can fuse

same size

Haplontic Life Cycle of Chlamydomonas

• Photosynthetic protist showing an early eukaryotic life cycle

• No mitosis in diploid phase

Resting spore withstands poor

conditions

Gametangium: cell that

produces gametes by

mitosis

Sporangium: cell that

produces spores by

mitosis

Haplontic Life Cycle of Ulothrix

Gametophyte: multicellular

haploid structure that produces

gametes

Isogametes fuse to form diploid

zygote

• 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

Spore: haploid cell that

can grow by mitosis

Applying Your KnowledgeApplying Your Knowledge

A.A. For For UlothrixUlothrix, spores are produced by, spores are produced byB.B. Growth of a gametophyte occurs byGrowth of a gametophyte occurs byC.C. For For ChlamydomonasChlamydomonas, spores are , spores are

produced byproduced byD.D. For For UlothrixUlothrix, gametes are produced by, gametes are produced by

1.1. MitosisMitosis

2.2. MeiosisMeiosis

3.3. Both Mitosis and Meiosis Both Mitosis and Meiosis

Diplohaplontic Life CycleDiplohaplontic Life Cycle

Haploid Phase

Diploid Sporophyte

Haploid Gametophyte Mito

sis

Diploid Phase

Mitosis

Gametes

Fertilization/SyngamyM

itosi

sMeiosis

Haploid Cells

in specialized

structuresZygote

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

Applying Your KnowledgeApplying Your Knowledge

A.A. Where is the sporophyte found?Where is the sporophyte found?

B.B. Zoospores are part of which phase?Zoospores are part of which phase?

C.C. Where is the gametophyte found?Where is the gametophyte found?

D.D. Where is the zygote found? Where is the zygote found?

1.1. Diploid PhaseDiploid Phase

2.2. Haploid PhaseHaploid Phase

3.3. Both Diploid and Haploid PhasesBoth Diploid and Haploid Phases

Diplontic Life Cycle in FernDiplontic Life Cycle in Fern

Haploid Phase

Diploid Phase

Mitosis

Gamet

es

Ferti

lizat

ion/

Syng

amy Meiosis

Haploid Cells

Zygote

Haploid Gametophyte Mito

sis

Diploid Sporophyte

Mito

sis

i n sp

ecial i ze d

st ructu

re s

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

Archegonium: organ that

produces eggs by mitosis

contain sporangia(singular: sorus)

Antheridium: organ that

produces sperm by mitosis

Antheridium: organ that

produces sperm by mitosis

Archegonium: organ that

produces eggs by mitosis

Sperm swim to archegonium and

one sperm fertilizes the egg

Applying Your KnowledgeApplying Your Knowledge

• If a fern species has 5 pairs of If a fern species has 5 pairs of homologous chromosomes, how homologous chromosomes, how many chromosomes would be found many chromosomes would be found in a(n)in a(n)– SporophyteSporophyte

– ArchegoniumArchegonium

– SporeSpore

– GametophyteGametophyte– Sporangium Sporangium (not including spores inside)(not including spores inside)

Diplontic Life Cycle in AnimalsDiplontic Life Cycle in Animals

Haploid Phase

Diploid Phase

Fert

iliza

tion

/Syn

gam

yZygote

Diploid Organism

Mito

sis

i n sex o

rga n

s

Gam

etes

Meiosis

Evolutionary TrendsEvolutionary Trends

• Reduced length of haploid phaseReduced length of haploid phase• Reduced amount of mitosis in haploid phaseReduced amount of mitosis in haploid phase• Increased amount of mitosis in diploid phaseIncreased amount of mitosis in diploid phase• Increased size of diploid adult organismIncreased size of diploid adult organism• Role of mitosis changes from reproduction in Role of mitosis changes from reproduction in

haploid phasehaploid phasegrowth in haploid growth in haploid phasephasegrowth in diploid phasegrowth in diploid phase

• Single cells Single cells Multicellular organisms Multicellular organisms• Increased tissue differentiationIncreased tissue differentiation• Longer-lived speciesLonger-lived species• Note that the role of meiosis and fertilization Note that the role of meiosis and fertilization

remains the same: to generate new remains the same: to generate new combinations by sexual reproduction combinations by sexual reproduction