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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