Download Development

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The Basis of
Development
From fertilized egg to
multicellular organism
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Cell Division:
increase in cell number
Differentiation:
cells becoming
specialized in structure
and function
Morphogenesis;
physical processes
giving an organism
shape
Morphogenesis: plants vs. animals
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Animals:
movements of cells and tissues are
necessary for 3-D form of the
organism
ongoing development in adults
restricted to differentiation of cells
continually replenished throughout
lifetime
Plants:
morphogenesis and growth of
overall size occur throughout
lifetime of plant; apical meristems
(perpetually embryonic regions),
responsible for plant’s continual
growth
Differential gene expression
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Differences between cells come from
differences in gene expression (genes
turned on or off), not from differing
genomes.
Evidence:
1- Genomic equivalence: all the cells
of an organism have the same genes
2- Totipotency: cells that can retain
the zygote’s potential to form all parts
of the mature organism (plant cells;
cloning)
3- Determination: restriction of
developmental potential causing the
possible fate of each cell to become
more limited as the embryo develops;
noted by the appearance of mRNA
Determination--->Differentiation
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Determination: as the embryo
develops the possible fate of
each cell becomes more limited
Differentiation: specialization of
cells dependent on the control of
gene expression
Induction: the ability of one
group of embryonic cells to
influence the development of
another; cytoplasmic
determinants that regulate gene
expression
Homeotic genes: genes that
control the overall body plan of
animals by controlling the
developmental fate of groups of
cells
Genetic cell death
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Apoptosis
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1. Programmed cell death is as
needed for proper development as
mitosis is.
Ex: Reabsorption of the tadpole
tail; formation of the fingers and
toes of the fetus requires the
removal of the tissue between
them; sloughing off of the
endometrium at the start of
menstruation; formation of the
proper connections (synapses)
between neurons in the brain
requires that surplus cells be
eliminated.
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programmed
cell death (“suicide genes”)
Apoptosis, Pt. II
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2. Programmed cell death is needed to destroy cells
that represent a threat to the integrity of the
organism.
Ex: Cells infected with viruses; waning cells of the
immune system; cells with DNA damage; cancer cells
Def: an•i•mal (n)
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Unique characteristics:
Heterotrophic eukaryotes; ingestion
Lack cell walls; collagen
Nervous & muscular tissue
Sexual; diploid; cleavage; blastula; gastrulation; larvae;
metamorphosis
Regulatory genes: Hox genes
Animal phylogeny & diversity,
I
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Monophyletic; colonial flagellated protist
ancestor
1- Parazoa-Eumetazoa dichotomy:
sponges (Parazoa)~ no true tissues; all
other animals (Eumetazoa)~ true tissues
2- Radiata-Bilateria dichotomy: Cnidaria
(hydra; ‘jellyfish’; sea anemones) &
Ctenophora (comb jellies)~ radial body
symmetry; all other animals~ bilateral
body symmetry (also: cephalization)
Animal phylogeny & diversity,
II
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3- Gastrulation: germ layer
development; ectoderm (outer),
mesoderm (middle), endoderm (inner);
radiata are diploblastic-2 layers; no
mesoderm; bilateria are triploblastic-all
3 layers
4- Acoelomate, Pseudocoelomate, and
Coelomate Grades: triploblastic
animals~ solid body, no body cavity
called acoelomates (Platyhelminthesflatworms); body cavity, but not lined
with mesoderm called
pseudocoelomates (Rotifers); true
coelom (body cavity) lined with
mesoderm called coelomate
Animal phylogeny & diversity, III
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5- Protostome-Deuterostome
dichotomy among coelomates:
protostomes (mollusks, annelids,
arthropods); deuterostomes
(echinoderms, chordates)
a) cleavage: protostomes~ spiral
and determinate; deuterotomes~
radial and indeterminate
b) coelom formation: protostomes~
schizocoelous; deuterostomes~
enterocoelous
c) blastopore fate: protostomes~
mouth from blastopore;
deuterostomes~ anus from
blastopore
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Embryonic
development/fertilization
Preformation~ until 18th century; miniature infant in sperm or egg
At fertilization/conception:
Acrosomal reaction~ hydrolytic enzyme action on egg jelly coat….
Fast block to polyspermy~ membrane depolarization prevents multiple
fertilizations….
Cortical reaction~ release of calcium causes hardening of egg outer layer and
creates a...
Slow block to polyspermy and...
Egg activation~ increases metabolic activity; protein synthesis
The Fertilized Egg & Cleavage
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Blastomeres~ resultant
cells of cleavage/mitosis
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Yolk~ nutrients stored in the
egg
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Vegetal pole~ side of egg
with high yolk concentration
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Animal pole ~ side of egg
with low yolk concentration
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Morula~solid ball of cells
Blastocoel~fluid-filled cavity
in morula
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Blastula~hollow ball stage of
development
Gastrulation
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Gastrula~ 2 layered, cup-shaped
embryonic stage
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3 Embryonic germ layers:
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Ectoderm~ outer layer; epidermis;
nervous system, etc.
Endoderm~ inner layer; digestive tract
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and associated organs; respiratory, etc.
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Mesoderm~skeletal; muscular; excretory,
etc.
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Invagination~ gastrula buckling
process to create the...
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Archenteron~ primitive gut
Blastopore~ open end of
archenteron
Organogenesis: organ
formation
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Blastodisc~ cap of cells
on top of yolk
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Primitive streak~
invagination of blastodisc
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Neural tube~ beginning
of spinal cord
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Somites~
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Neural crest~ bones
vertebrae and
skeletal muscles
and muscles of skull
Amniote embryos
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Extraembryonic
membranes:
•yolk sac
(support; circulatory function)
•amnion
(fluid-filled sac; protection)
•chorion
(placenta formation)
•allantois
(nitrogenous waste)