1. Evo-Devo Developmental Patterns and Evolutionary Patterns
Studying Cell Patterns

2. 10.4 Developmental Patterns and evolution
Similar developments indicate evolutionary relationships
“Ontogeny recapitulates Phylogeny” Ernst Haeckel
Dev’t is a replay of ancestry
Haeckel noticed that vertebrate embryos pass through a series of similar stages in early development, and argued that there was a good reason for this. As an organism evolves, he reasoned, it does so by taking on new stages to its process of embryonic development. Therefore, as an organism passes through embryonic development it actually re-traces every stage of its evolutionary ancestry. This idea became known as "Ontogeny recapitulates Phylogeny," which literally means "Development is a replay of Ancestry.“ this is no longer supported in full, but still has a reasonable basis for the relatedness between organism. Ernst Haeckel’s sketches were denounced as fraudulent during his own day but textbook’s to this day continue to publish the pictures.

3. How are organisms related based on morphogenesis?
P 269 as a picture

4. How is morphogenesis determined? What are the literal instructions?

5. 10.6 Birth Defects Causes: Polydactyl- extra digits
defective/mutant gene
environmental factors acting on developmental genes
Polydactyl- extra digits
Spina bifida- part of neural tube does not close completely
Anencephaly- brain does not completely develop- exposed brain degenerates and top of skull fails to form

6. How do we know?
DNA  RNA  proteins (responsible for phenotype/what we see expressed as a trait)
All DNA is present in ALL cells
Not all DNA is being “read”
there4, only certain proteins are made
RNA is the intermediary between DNA and protein
If RNA is present, that is the proof that the DNA is being “read”

7. DNA-RNA Hybridization
Shows what DNA/genes are being expressed
DNA is made single-stranded and tagged with flourescence
Labeled DNA is mixed with embryonic cells
Under microscope, can see if DNA bound RNA

8. 10.8 genetic equivalence of differentiating cells
What happens to unused genes after cell differentiation?
Two theories:
1. Selective- Gene- Loss Hypothesis
differentiating cells lose some genes
2. Gene Equivalence Hypothesis
All cells have same genes but only some are active during differentiation. Genes are not lost- just not expressed.

9. Which Idea is Correct? 2 experiments:
1952- Briggs and King (Fig )
Blastocyst v. skin cell
Followed soon after by John Gurdon’s Experiment
Tadpole v skin cell
CONCLUSION:
All cells are genetically equal.
No genes are lost.
Differentiation restricts the expression of some genes.

10. 10.9 Determination and Differentiation
Many embryonic cells are committed to their fate long before differentiation ever begins.
Proteostomes tend to be earlier deuterostomes
Snail vs. frog exp’ts
Sometimes cells determine independently
Other cells communicate and affect each other’s determination
2007 video : skin cell SCNT (9:29)

11. 2 separated frog cells- each develop into tadpole
Snail cells were irreversibly determined already- would not develop into whole snail
*In the frog the cells adjust. The snail could not adjust because cell fate determined early in development
WHY?
Proteins & RNA distribute unevenly- separated into different cells through cleavage

12. 10.11 Cell-Cell Interactions:Embryonic Induction
Differentiation is more flexible in vertebrate embryos
Demonstrated by Spemann and Mangold, 1920
Cells moved around in embryo responded to other nearby cells and altered determination
Example: skin ectoderm cells moved to dorsal region above notchord became neural tube instead of skin
This process is called Embryonic Induction
Early blastula but not late gastrula

13. 10.11 Cell- Cell Interaction: Role of Notochord
Spemann and Mangold
Demonstrated that the notochord is the source of the inducing signal
Experiment: tissue determined to become notochord was transferred to another organism 2nd notochord grew  second larva formed!
Later experiments:
Cell contact not required
Inducing proteins are released: chordin and noggin
Chordin- notochord formation, anterior-posterior axis
Noggin- formation of dorsal structures, ventral ectoderm becomes nerve tissue