Development of Multicellular Organisms Flashcards
Genome of all cells in an organism are ____ but expression of genes is ____
identical
different
what controls development
differential gene expression
four major phases in development
- cell division and proliferation: producing many cells from one
- cell specialization/differentiation: creating cells with different characteristics
- cell interaction: influences behaviors of other cells
- cell movement/migration and rearrangement: forms layers which give rise to structures such as tissues and organs
*all happens simultaneously in different parts of the developing embryo
development
- cells have a memory
- cells retain record of signals their ancestors received during embryonic development
- genes expressed by cell depend on environment, both present and past
functional interchange of homologous proteins:
homologous proteins are functionally interchangeable
- basic machinery for development similar for all organisms
- e.g. mouse lacking cerebellum gene –> cerebellum gene from fly inserted into mouse –> mouse developed cerebellum
conserved mechanisms for development
- after fertilization the zygote divides rapidly
- results in formation of many small cells that are dependent on food stored in egg by the mother
- genome is inactive initially
- later genome becomes activated and cells divide and cohere to form a blastula
- blastula then undergoes massive rearrangements to form gastrula
blastula
ball of cells surrounding a hollow cavity
gastrula
blastula that undergoes massive rearrangements that has 3 major layers
blastula consists of a sheet of ______ facing the external medium; which gives rise to the ____
sheet of epithelial cells
ectoderm
ectoderm
precursor of nervous system and epidermis
“attract-o-derm: everything that many people find attractive (hair, skin, eyes, brain)”
part of epithelial sheet becomes tucked into the interior which gives rise to the
endoderm
endoderm
precursor of gut, lung, and liver
“endternal organs: most of the internal organs”
group of cells that move into the space between the ectoderm and endoderm (break off from the endoderm) gives rise to the
mesoderm
mesoderm
precursor of muscle and connective tissues
“means of getting around: movement, cardiovascular system, skeleton and muscles “
gastrulation
transformation of the blastula, a hollow sphere of cells into a layered structure with a gut
50 percent genes in a fruit fly nematode worm, and human have recognizable ____ in the other species
homologs
higher organisms have several homologs of the same gene
gene duplication
gene regulatory proteins
most important for development
instructions for producing a multicellular animal is contained in the
non-coding regulatory DNA sequences associated with each gene
_____ sequences in DNA similar in most organisms but _____ sequences make one organism different from another and provide uniqueness
coding
non-coding
cells make developmental decisions long before they should any outward signs of _____
differentiation
e.g. appearance of the red cell is the final act
determined
cells that are fated to develop into a specialized cell type despite changes in environment
e.g. fated to be a red cell –> if put in another environment –> still becomes a red cell
completely undetermined (not determined)
cells that can change rapidly due to alterations in environment
committed
cells that have some attributes of a particular cell type but can change with environment
memory of positional values
- before acquiring a particular fate, cells express genes that are markers of their location e.g. they are ‘regionally determined’
- position specific character of cell called positional value
- cells retain ‘memory’ of positional value
cellular differentiation:
asymmetric division (e.g. development of germ cells) and inductive signaling
asymmetric division
-significant sets of molecules distributed unequally between daughter cells
inductive signaling
- definition: induction of a different developmental program in select cells in a homogeneous group leading to altered character
- cells born the same can become different due to change in environment after birth (different molecules induced)
- these molecules then directly or indirectly alter the pattern of gene expression between the 2 cells
- most important environmental cues are signals from neighboring cells
- few cells closest to the source take on induced character - signal is limited in time and space
types of signals in inductive signaling:
- short range: cell-cell contacts
- long range: substances that can diffuse through the extracellular medium
morphogen
- definition: long rand inductive signal that imposes a pattern on a field of cells
- exert graded effects by forming gradients of different concentrations
- each concentration can direct the target cells into a different developmental pathway
- need an “on” and “off” system
- antagonists or extracellular inhibitors bind to the signal or its receptor and block interaction
what forms gradients:
- localized production of an inducer that diffuses away from its source
- localized production of an inhibitor that diffuses away from its source and blocks the action of a uniformly distributed inducer
p granules
form germ cells
lateral inhibition and positive feedback
steps:
- system starts off homogeneous and symmetrical
- environment imposes weak asymmetry
- positive feedback amplifies effect
- broken asymmetry is ‘all or none’ phenomenon
- irreversible: once achieved, external signal becomes irrelevant
e. g. delta-notch signaling (uses lateral inhibition)
