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  • 3. A Characteristic of Living things Growth, Division, Reproduction
  • 4. New Terms: • Development – progress through lifetime • Growth – increase in size, volume, mass • Morphogenesis – development of shapes • Epigenesis – development from a formless zygote • Differentiation – cells become different from each other • Determination – fate of cells is set (before differentiation), usually at gene control level • Induction – One tissue or substance causes determination, then differentiation, of other cells
  • 6. EVOLTUION OF EMBRYOS •Requires multicellularity •Only becomes embryology when cells are differentiated. •Follows a common pattern in the Animal Kingdom
  • 7. Stages in Embryology Animal Examples
  • 8. The Egg • Large, sessile gamete • Yolk – the phospholipid lecithin • Haploid nucleus (notice timing for humans and Ascaris) • Oolemma – two membranes plus jelly layer • Jelly layer -- Hyaluronic Acid and Proteins • Cortical granules – vesicles in cortex
  • 9. The Sperm • Small, motile gamete • Flagellated in animals and lower plants • Haploid nucleus • Acrosome – specialized cytoplasmic vesicle for digesting jelly layer (hyaluronidase and proteases) and for attaching to Oolemma (bindin)
  • 10. Fertilization • Sperm activated by egg hormones (gynagamones) • Formation of Acrosomal Process (microfilaments) • Release of hyaluronidase and proteases • Bindin attach to bindin recognition site on oolemma
  • 11. Egg Activation • Depolarization of membrane • Evacuation of cortical granules • Elevation of vitelline membrane (separation of vitelline membrane from egg cell membrane in oolemma) • Blocking of all other bindin sites • Activation of metabolism in cytoplasm • Completion of meiosis in some organisms
  • 12. Early cleavage • First cleavage – Two-cell stage • Second cleavage – Four-cell stage • Additional cleavages in ball shape • Morula • Blastula – first morphogenetic movements (cells migrate to form hollow ball) • Blastocoel (space) and Protoderm (tissue)
  • 13. Gastrulation • Second Morphogenetic step (first is formation of the blastula). • Tissues MOVE relative to each other and relative to their position in the embryo! • Different cells move different amounts and change shape by different amounts. • Protein gradients in embryo control this. • HOX and Homeobox genes in animal kingdom
  • 14. Morphogenesis Example of invagination Cells change shape Coordinated by position Role of Cytoskeleton
  • 15. Early Cleavage Differences • Protostomes – Spiral cleavage – Determinate – Mosaic pattern – Blastopore  mouth – Arthropods, mollusks, annelids • Deuterostomes – Radial cleavage – Indeterminate – Regulated development – Blastopore  anus – Echinoderms, chordates
  • 16. Blastula Differences • Small eggs – symmetrical blastula (Echinoderms and Mammals) • Large eggs – asymmetrical blastula (Amphibians, Reptiles, Birds) • Animal Pole – active side  ectoderm • Vegetal Pole – inactive  endoderm
  • 17. Gastrulation in Frog • Morphogenesis: invagination • Epiboly and Involution for asymmetrical eggs • Triploblastic – three tissue layers – Ectoderm – outer skin, CNS in vertebrates – Endoderm – lining of the gut – Mesoderm – inner organs and tissues – Coelom – body space in proto- and Deuterostomes.
  • 18. Notocord in Chordates • First tissue to fully differentiate • Forms in mid-dorsal mesoderm (chordamesoderm) • Induces formation of neural tube and cranial space in nearby ectoderm (dorsal side) • Replaced by spinal column (cartilage and bone from mesoderm) in vertebrates
  • 19. Differentiation of Mesoderm • Mid-dorsal – chordamesoderm • Dorsal – somites – segmented parts of body • Intermediate – thin layer, contributes to kidney and/or testicular ducts (labeled “nephrotome” in previous slide) • Lateral Plate – two sheets join at mid-ventral line – Somatic – body side – Splanchnic – surroundings of gut – Coelom – body space between two layers of mesoderm
  • 20. Pattern formation • Studied first in Drosophila • HOX and Homeobox genes found throughout animal kingdom • Frequent repeated inductions followed by determination, then differentiation • Stimulates morphogenesis, part of development
  • 21. Chick • 3-D slide from dorsal side • Note: – Somites, – Neural tube and cranial space – Notocord • Compare to Frog slices
  • 22. CLONING • Dedifferentiation of carrot cells. • Demonstration that frog cells are not terminally differentiated. • More difficult in mammals!!
  • 23. Summary • Development is part of a life cycle • Involves mitosis for nuclear division • Changes in control of DNA cause differentiation (different proteins made in different concentrations) • Genes and development steps are regulated by other genes throughout life
  • 25. Reproduction • To “produce again” • Life cycle includes both diploid and haploid phases • You, as an individual, are the diploid phase of a life cycle • Emphasis on phases leads to classification of life cycles
  • 26. Generalized Life Cycle Diploid phase Haploid phase meiosisFertilization/symgamy zygote gametes Diploid adult?? Haploid adult??
  • 27. Representative Examples • Chlamydomonas – haplontic (haploid dominant) life cycle, single celled • Ulothrix – haplontic life cycle, filamentous (colony?) • Ulva – diplohaplontic life cycle, multicellular in both haploid and diploid phases, phases equal. • Fern – diplontic (diploid dominant) life cycle • Animal Kingdom – extreme diplontic life cycle; learn Echinoderm, Ascaris, human
  • 28. Haploid Phase Diploid Phase HAPLONTIC STYLE OF LIFE CYCLE
  • 29. Chlamydomonas • Protist • Chloroplast • Haplontic life cycle (Haploid dominant) • No mitosis in diploid phase of cycle • Represents very early Eukaryotic life cycles
  • 30. Chlamydomonas
  • 31. ULOTHRIX • Haplontic life cycle • “Multicellular” in haploid phase (colonial?) • Both growth and asexual reproduction by mitosis in haploid phase. • Diploid phase (resting spore) can only perform meiosis (no mitosis in diploid phase)
  • 32. New Terms • Gametophyte – the gamete-producing plant. This describes a multicellular HAPLOID phase in plant life cycles. This plant produces gametes by MITOSIS (chromosome number stays the same!). • Spore – a haploid cell that will divide by mitosis (usually to produce a gametophyte).
  • 33. More New Terms • Gametangium – in Ulothrix and many similar algae, it is a specialized cell that produces gametes by mitosis. • Sporangium, or zoosporangium – a specialized cell that produces spores (zoospores) by mitosis. • Zoospore – a spore that is flagellated.
  • 34. Diploid phase Resting spore only Haploid phase Includes spores, a multicellular filament (gametophyte), and gametes Ulothrix Haplontic style life cycle
  • 35. Alternation of generations • Ulva is our example • Introduction of mitosis in the diploid phase! • Eons of evolutionary time to develop • Loss of asexual reproduction in the haploid phase for some species. • Mitosis still in haploid phase for growth and production of gametes.
  • 36. New Terms • Sporophyte – the spore producing plant. This is the multicellular DIPLOID plant. It produces spores by MEIOSIS (chromosome number reduced from diploid to haploid). • Sporangium – specialized cells or ORGAN (multicellular structure) that produces spores by meiosis. Located on the sporophyte.
  • 37. Emphasis of Diploid Phase • Ferns, Conifers, Flowering Plants • Gametophyte becomes less important in the life cycle (smaller than sporophyte and with a shorter lifetime). • Sporophyte develops complex tissues and organs.
  • 38. New Terms for Fern • Thalus – name for the gametophyte (n). • Archegonium – gametophyte (haploid) organ that produces eggs by mitosis. • Antheridium – gametophyte (haploid) organ that produces sperm by mitosis. • Sorus – structure on underside of sporophyte leaf that contains many sporangia (diploid) that produce spores by meiosis.
  • 39. Evolutionary Trends • Shift in emphasis from haploid dominant to diploid dominant life cycles. • Shift from haploid to diploid organisms. • Single to multicellular; increased tissue differentiation; longer lives • Emphasis on mitosis for reproduction in haploid phase (asexual) to use of it for growth, then growth in diploid phase • Meiosis/fertilization ONCE per life cycle (sexual reproduction)
  • 40. SUMMARY • Switch in emphasis from dominant haploid to dominant diploid phases. • Development of multicellularity, then of tissue differentiation. • Role of MITOSIS undergoes significant change. • Roles of meiosis and fertilization do NOT change.