Title: BIL 160 - Alternation of Generations
Headings: Going from
2n

Sexual Encounters
of the Floral Kind
Animal Sex is Simple
Plant Sex is...Complicated.
Evolution of the Alternation of Generations
Terminology: A typical fern (tracheophyte) will illustrate.
Sporophyte (2n)
Sporophyll (2n)
Sporangium (2n)
Spore (n)
Gametophyte (n)
Multicellular Sex Organs
Which Sex?
Zygote (2n)
New Sporophyte (2n)
If Animals Underwent Alternation of Generations: A Disturbing Analogy
I. The Sporophyte Generation
An Imaginary, Dioecious Animal Sporophyte
The Sporophyte Produces Spores via Meiosis
Spores are Released
Sporophytes Also Can Be Monecious or Bisexual
II. The Gametophyte Generation
Male and Female Gametophytes
Male Gametophyte (n): Antheridia Produce Sperm
Female Gametophyte (n): Archegonia Produce Ova
Sperm and Ova Ready...
Go Sperm, Go!
III. Return of the Sporophyte
A Pregnant Pause
This Will Not End Well for Smurfette
Evolution: Gametophyte vs. Sporophyte
I. Evolutionary Progression: Long-lived Gametophyte, Ephemeral Sporophyte
The Bryophyte Gametophyte is the Perennial Generation
Bryophyte Gametophytes
Bryophyte Gametophytes can be
Monoecious or Dioecious
II. Evolutionary Progression: Long-lived Sporophyte, Ephemeral Gametophyte
The Tracheophyte Gametophyte is the Annual Generation
Seedless Tracheophyte Gametophytes
Seed Plant Gametophytes are Small and Dioecious
Seed Plant Gametophytes: Male
Seed Plant Gametophytes: Female
Life Cycle of a Conifer
A Pine Tree Produces Male Gametophytes (pollen) in Male Cones
A Pine Tree Produces Female Gametophytes (inside ovules) in Female Cones
Life Cycle of a Flowering Plant
A Flower is a Cluster of Sporophylls
A Flowering Plant Produces Male Gametophytes (pollen) in Anthers
A Flowering Plant Produces Female Gametophytes (inside ovules) in Ovules
III. Evolutionary Progression: Ephemeral Gametophyte, Long-lived Sporophyte
Ephemeral Bryophyte Sporophyte: Liverworts
Ephemeral Bryophyte Sporophyte: Mosses
Long-lived Seedless Tracheophyte Sporophyte: Club Mosses
Long-lived Seedless Tracheophyte Sporophyte: Ferns
Long-lived Seedless Tracheophyte Sporophyte: Cycads
Long-lived Seedless Tracheophyte Sporophyte: Ginkgos
Long-lived Seedless Tracheophyte Sporophyte: Conifers
Long-lived Seedless Tracheophyte Sporophyte: Anthophytes
And That's How Plants Do.
II. TERMS RELATED TO THE (DIPLOID) SPOROPHYTE GENERATION:

Content: ...and the cycle continues. Not quite so simple. x
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The change in ploidy from parent to offspring is known as the Alternation of Generations . sporophyte ( 2n) ---> gametophyte ( n) ---> sporophyte ( 2n) ---> gametophyte ( n) ---> sporophyte ( 2n) ---> etc. Land plant alternation of generations is said to be heteromorphic. x
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By IvoShandor via Wikimedia Commons
Evolution of the Alternation of Generations
A land plant is either a
non-vascular bryophyte (more primitive)
Gametophyte (n) is the dominant life cycle stage. Sporophyte (2n) is small and ephemeral /seasonal. vascular tracheophyte (more derived)
Sporophyte (2n) is the dominant life cycle stage. Gametophyte (n) is small and ephemeral /seasonal. (The "dominant" life cycle stage is larger and more conspicuous.)