Development of Multicellular Organisms
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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