Entwickslungmechanik Developmental Mechanisms Wilhelm Roux: “We must not hide from ourselves the...
-
Upload
tyler-anthony -
Category
Documents
-
view
215 -
download
0
Transcript of Entwickslungmechanik Developmental Mechanisms Wilhelm Roux: “We must not hide from ourselves the...
Wilhelm Roux:
“We must not hide from ourselves the fact that the causal investigation of organisms is one of the most difficult, if not the most difficult, problem which the human intellect has attempted to solve… since every new cause ascertained only gives rise to fresh questions regarding the cause of this cause.”
Experimental Embryology
Experimental embryology had its beginnings in the testing of hypotheses of cell specification
Experimental Embryology
August Weismann’s Germ Plasm Theory1883First testable hypothesis of cell
specificationDeterminants within zygote were
partitioned into cells as development proceeded
Experimental Embryology Weismann hypothesis
Egg and sperm provide equal chromosomal contributions to embryo
Chromosomes carried the inherited determinants The chromosomes/determinants were somehow
differentially distributed to embryonic cells Only the germ cells received all determinants
(germ plasm)
Experimental Embryology
Testing Weismann’s HypothesisEach half of a developing frog embryo is
derived from one cell of the two cell staged embryo
Each blastomere are the two cell stage must therefore contain left and right determinants
Experimental Embryology
4 Categories of Experiments
Defect experiment
Isolation experiment
Recombination experiment
Transplantation experiment
Experimental EmbryologyWilhelm Roux (1888) 1st to test Weismann’s hypothesis.Roux’s defect experiment supported mosaic development and partitioning of determinants.
Experimental Embryology
Hans Driesch’s (1892)Isolation Experiment: Dissociation of 4 and 8 cell sea urchin embryos demonstrated regulative development.
Dissociation was accomplished by incubation in Ca free water implies that Ca is important for cell adhesion
Experimental Embryology Roux’s experiment suffered from an experimental
design flaw
By killing one of the two blastomeres, but not removing it, the remaining dead cell prevented rearrangement of the living cells to produce a normal embryo
Driesch’s experiment did not suffer from this flaw since he had separated all the cells of the embryo
McClendon (1910) repeated Driesch’s experiment in frogs with the same result