Life Sciences 2 September 8, 2010 Embryology II: Evolution & Development Prof. Daniel E. Lieberman Office hours: Tue 1-2 & by appt! (Peabody 53)
ANNOUNCEMENTS Labs : Start this week! Problems : Dr Carr ([email protected]) My office hours: Tuesdays 1-2 & by appt (Peabody 53)
embryos represent basic body plan that can be widely modified ...an old idea whose origins helped Darwin formulate his theory Phylotypic stage
Last lecture: 2. What is the basic body plan? 1. How do we go from a single cell to awhole body?
1. Evolutionary changes that generate complexity occurred from many, many intermediate steps.
Two solutions to the “blind watchmaker” problem 2. The processes by which development occur permit & promote evolutionary change and complexity Body has many parts (modules ) that develop via a hierarchical (branching) process with many interactions between modules Modules Genes Cells Germ layers Segments Etc… Interactions Growth Movement Induction Etc.. Interactions between modules cause integration: parts become combined into whole
An example of integration Folding of body walls to create tube-shaped embryo coelom Gut tube Neural tube Paraxial mesoderm Splanchnic mesoderm Somatic mesoderm
AN IMPORTANT POINT: Variation happens Variation in modules Variation in how modules interact e.g. # of somites e.g. interactions among somites and other tissues NOVELTIES THAT FIT & WORK TOGETHER Genetic mutations
An analogy Modules (different Lego™ blocks) Interactions (how you snap them together) Because Legos all share basic bits that snap together, they can be endlessly recombined in novel ways to create VARIATIONS that often fit together and “work” Selection can then act on this variation
And, since development is hierarchical with many stages/units/interactions, there is great opportunity for change (descent with modification)
-bones, muscles & nerves that interconnect -limbs -heads Let’s see how evolutionary changes to development created:
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- Fall '10
- Developmental Biology, Neural tube, Mesoderm