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Types of Development

overview of development - control of gene expression >> specialization 

  • fungi development - only reproductive cells are specialized
    • higher fungi - basidiomycetes/ascomycetes, produce pheromones that influence other cells
    • usually just long cell filaments not completely separated from each other
    • mostly a growth process, not specialization
  • plant development - variety of specialized cells organized into tissues/organs
    • environment determines exact array of tissues
  • animal development
    • environment doesn’t affect animals as much as plants

vertebrate development - cells divide rapidly, forms shape, organs 

  • cleavage - initial period of cell division
    • zygote divides >> blastomeres (small cells) >> ball of cells made
    • no increase in size for embryo
    • animal pole - end of zygote where blastomeres go on to form external tissues
    • vegetal pole - end of zygote where blastomeres go on to form internal tissues
    • point where sperm enters egg = future belly
    • gene transcription begins after about 12 divisions
  • formation of the blastula - creates hollow ball of cells called blastula
    • aka blastocyst in mammals
    • tight junctions join outer blastomeres
    • Na+ pumped into space between cells to draw water into center of blastula
  • gastrulation - creates main axis of vertebrate body
    • lamellipodia used by cells to crawl over other cells
    • converts blastula into symmetrical embryo w/ central gut
    • has 3 germ layers (endoderm, mesoderm, ectoderm)
    • endoderm - forms tube of gut, will form most internal organs
    • ectoderm - cells on outside, will form skin/nervous system
    • mesoderm - will form notochord, bones, blood vessels, muscle
  • neurulation - ectodermal cells thicken, contract actin filaments to make neural tube
    • neural tube - will form brain, spinal chord
  • cell migration - cells move to form distant tissues
    • neural crest - cells that pinch off from neural tube to form sense organs
    • somites - cells move from central muscle blocks, form skeletal muscles
    • receptor proteins change cytoskeleton of cells to stop them from moving after they arrive at the correct locations
  • organogenesis/growth - basic body plan already laid out
    • tissues develop into organs
    • embryo grows to be 100x larger

insect development - produces 2 types of bodies 

  • larva - tubular eating machine, forms flying sex machine through metamorphosis
  • maternal genes - development begins before fertilization, w/ egg construction
    • specialized nurse cells move own mRNA into particular locations in egg
    • zygotic genes don’t determine first part of development
  • syncytial blastoderm - contains about 6000 nuclei
    • formed by 12 nuclear divisions w/o cytokinesis
    • membranes form between nuclei, forming larva (tubular body)
  • larval instars - total of 3 stages (instars) occur over about 4 days
    • exoskeleton prevents growth, must be shed so growth can occur
  • imaginal discs - cells that play no role in larva life, but forms important parts of adult fly’s body
  • metamorphosis - larva >> pupa after last larva stage
    • larval cells break down to release nutrients that fuel growth of imaginal discs
    • imaginal discs associate to form body of adult fly

plant development - plant cells cannot move due to cellulose walls 

  • meristems - self-renewing cells that grow outward
  • body made from types of modules (leaves, roots, branch nodes, flowers) dependent on environment
  • early cell division - off-center division, makes smaller cell w/ dense cytoplasm (future embryo)
    • suspensor - links embryo to nutrients of seed
    • cells near suspensor form roots
    • cells away from suspensor form shoots
  • tissue formation - 3 basic tissues form w/o cell mov’t
    • epidermal cells - outermost cells
    • ground tissue cells - interior cells, will form food/water storage
    • vascular tissue - cells at core of embryo
  • seed formation - flowering plant embryo makes 1-2 coyledons (seed leaves)
    • development pauses, embryo surrounded by nutritive tissue
    • forms seed (resistant to drought, unfavorable conditions)
    • disperses embryo to distant areas
  • germination - occurs in response to environmental changes
    • embryo starts development again to extend roots downward, shoots upward
  • meristematic development - apical meristems form cells needed for leaves/flowers
  • morphogenesis - microtubules direct cellulose deposition, orientation of fibers, direction of growth

nematode development - made up of about 959 somatic cells, 1 mm long 

  • entire genome mapped out as series of overlapping fragments
  • transparency allows viewing of cell mov’t during development
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