Patterning invertebrate embryos
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How do you identify genes involved in the developmental process?
use of forward genetics mutation > gene > protein > function use of mutagenesis to create random mutations in the genome inbreed the mutant gemone use phenotype analysis to find the function of the gene clone the gene to find molcule identity analyse the function of the gene product
what are the cleavage divisions of drosophila (30, 70, 90, 2hrs, 3hrs
30 - fusion of sperm and egg nuclei 70 - nuclear division creating the synctium 90 - nuclei migrate to the periphery of cytoplasm 2 hrs - synctial blastoderm forms 3hrs - cellular blastoderm forms
how do you recognise the anterior end of a drosophila egg?
micropyle - a nipple shaped sturcture in the tough external coat surrounding the egg
where do sperm enter the drosphila egg?
the micropyle
what occurs after fertilisation and fusion of nuclei in drosophila?
a series of mitotic divisions no cleavage of cytoplasm and no formation of cell membrane to separate nuclei
what forms after 12 nuclear division in drosophila development?
formation of the synctium, approx 6000 nuclei present in the cytoplasm
what does formation of the synctium in drosophila allow?
allows large molecules to to diffuse between nuclei during the first 3hrs of development
what happens at synctial stage of drosphila?
small no of nuclei move to the posterior end and become surrounded by the cell membrane to form pole cells
What do pole cells in drosophila do?
pole cells give rise to germ cells from which gametes develop
what happens after 9 nuclear divisions in drosophila?
nuclei move to the periphery to form the synctial blastoderm
what is the synctial blastoderm in drosophila development?
a superficial layer of nuclei and cytoplasm which surrounds a central mass of yolky cytoplasm, membranes grow in from the surface to enclose the nuclei and form cells
what does the blastoderm in drosophila give rise to?
somatic cells of the embryo
what are the three germ layers?
ectoderm, endoderm, mesoderm
where is the mesoderm located in drosophila?
in the ventral region
what is the future midgut derived from in drosophila?
2 regions of the prospective endoderm 1 at anterior and one at posterior end of the embryo
when do drosophila endodermal and mesodermal tissues move to their future positions?
during gastrulation, this leaves the ectoderm as the outer layer
when does gastrulation start in drosophila?
3hrs after fertilisation
how is the the future mesoderm of drosophila formed? how is it internalised? what does it eventually give rise to?
at ventral region it invaginates to form a furrow along the ventral midline internalised by formation of a mesoderm tube where the cells separate from the surface layer of the tube and migrate under the ectoderm to internal locations later gives rise to muscle and other connective tissues
what does each germ layer become?
a unit of lineage, once cells have been specified to one fate they all of its descendants will adopt this fate
where in insects does the main nerve chord lie?
ventrally
in drosohila after the invagination of the mesoderm, what is formed?
the nervous system
how is the nervous system of drosophila formed?
ectodermal cells in the ventral region leave the surface individually and form a layer of prospective neural cells between the mesoderm and the outer ectoderm
how and when is the gut formed in drosophila?
at the same time as nervous system formation , 2 tubular invaginations develop at the future posterior and anterior midgut. they grow inward toward each other and fuse to form the endoderm of the midgut. the ectoderm is dragged inward behinds the tubular invaginations to form the foregut and hindgut
what does the outer ectoderm develop into in drosophila?
the epidermis, ectoderm continues to divide during gastrulation but the mesoderm does not