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Evolution of Development. What is the developmental genetic basis of homologous structures?. How is development altered to give rise to new morphological structures?. What are the evolutionarily important genes that direct development?. Homeotic ( Hox ) Genes are - PowerPoint PPT Presentation
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Evolution of Development
How is development altered to give riseto new morphological structures?
What are the evolutionarily important genes that direct development?
What is the developmental genetic basisof homologous structures?
Homeotic (Hox) Genes areConserved Among Metazoans
1. Hox genes are organized in gene complexes
2. Temporal and spatial collinearity is known forHox genes
3. Hox genes code for regulatory proteins that regulate the transcription of other genes
Hox genes specifysegmental Identity
Phylotypic Stage
Mutational analysis of Hox genes
Ubx mutant
Transformation of T3 and A1 into T2 because UBX
does not repress expressionof T2 Hox genes
T3A1
Tribolium (flour beetle) with all 8 Hox genes mutagenized
Hox gene expression is correlated with segment identity
Flower Development: ABC gene expression in Arabidopsis
Hox Genes and Morphological Evolution
• Change in gene number
• Change in spatial expression
Evolution of Regeneration
What explains the distribution of regeneration among organisms?
- Adaptive?- Inherit to all metazoans
or independentlyderived?
Evolution and Development
Regeneration is Phylogenetically Widespread
Anuran Tail Planeria
Regeneration: Adaptive?
• Seemingly, the ability to regenerate should benefit individuals of a population (i.e. is adaptive).
• Can you think of a way to test the idea that regeneration is adaptive?
Hermit Crabs regenerate their anteriorand posterior limbs. However, the frequencyof regeneration is much higher for anteriorlegs (83% vs 21%).
From Morgan 1898 and Needham 1961
Regeneration: Inherent?
• Much of what is accomplished during regeneration is first accomplished during
embryonic development (same mechanisms are deployed).
• Can you think of a way to test the idea that regeneration is inherent?
Observations Supporting the Idea that Regeneration is Inherent
• Phylogenetically widespread• Lost between closely related species• Aspects of regeneration are similar among
organisms in a developmental sense• Some organisms that can not regenerate
body parts, do so partially during development.
Epimorphic Regeneration: The Blastema is Very Similar Among Unrelated Taxa
Regulation andEvolution of EpimorphicRegeneration
• Loss of regeneration may reflect genetic changes that are associated with evolutionary changes:
– With respect to amniote vertebrates:• Water to land transition• Poikilothermy to homothermy• Loss of metamorphosis• Evolution of immune system
Why Not Regeneration?Why don’t we observe it more?
However, there is variation among amphibians
• - Can regenerate limbs as immature larvae
• - Loses ability to regenerate at metamorphosis
• Adults regenerate a cartilagenous spike after limb amputation.• Is the generation of a spike an
adaptation?
Unlike salamanders, Xenopus has limited regenerative potential
100% regenerate spikeafter radia-ulna amputation
80% regenerate spikeafter humerous amputation
0% regenerate spikeafter complete amputation
Growth Rates
No legs amputated 0.55 9.54 10.2
1 leg amputated 0.54 9.0 9.54
2 legs amputated 0.53 7.5 8.8
Day 0 1 month 4 months
* Weights are in grams
The spike supportsnuptial pad tissue development in males.
2 of 3 males with1 regenerated
radia-ulna spike were able to successfully
amplex and matewith a female.
• The results suggest that spike regeneration maybe adaptive.
• But why did Xenopus frogs presumably loose the ability to reform perfect limbs?