evo-devo developmental patterns and evolutionary patterns studying cell patterns

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

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Page 1: Evo-Devo Developmental Patterns and Evolutionary Patterns Studying Cell Patterns

Evo-DevoEvo-DevoDevelopmental Patterns

and Evolutionary PatternsStudying Cell Patterns

Page 2: Evo-Devo Developmental Patterns and Evolutionary Patterns Studying Cell Patterns

10.4 Developmental Patterns and evolution• Similar developments indicate

evolutionary relationships• “Ontogeny recapitulates

Phylogeny” Ernst Haeckel

– Dev’t is a replay of ancestry

Page 3: Evo-Devo Developmental Patterns and Evolutionary Patterns Studying Cell Patterns

How are organisms related based on morphogenesis?

Page 4: Evo-Devo Developmental Patterns and Evolutionary Patterns Studying Cell Patterns

How is morphogenesis determined? What are the literal instructions?

Page 5: Evo-Devo Developmental Patterns and Evolutionary Patterns Studying Cell Patterns

10.6 Birth Defects

• Causes: – 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

Page 6: Evo-Devo Developmental Patterns and Evolutionary Patterns Studying Cell Patterns

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”

Page 7: Evo-Devo Developmental Patterns and Evolutionary Patterns Studying Cell Patterns

DNA-RNA Hybridization• Shows what DNA/genes

are being expressed• DNA is made single-

stranded and tagged with flourescenceflourescence

• Labeled DNA is mixed with embryonic cells

• Under microscope, can see if DNA bound RNA

Page 8: Evo-Devo Developmental Patterns and Evolutionary Patterns Studying Cell Patterns

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.

Page 9: Evo-Devo Developmental Patterns and Evolutionary Patterns Studying Cell Patterns

Which Idea is Correct?• 2 experiments:– 1952- Briggs and King (Fig.

10.19)• 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.

Page 10: Evo-Devo Developmental Patterns and Evolutionary Patterns Studying Cell Patterns

10.9 Determination and DifferentiationDetermination

• 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

– http://www.youtube.com/watch?v=LsxBhBsLNg8

Page 11: Evo-Devo Developmental Patterns and Evolutionary Patterns Studying Cell Patterns

• 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?WHY?Proteins & RNA distribute unevenly-

separated into different cells through cleavage

Page 12: Evo-Devo Developmental Patterns and Evolutionary Patterns Studying Cell Patterns

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

Page 13: Evo-Devo Developmental Patterns and Evolutionary Patterns Studying Cell Patterns

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