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Developmental Biology and Evolution 佟超 浙江大学生命科学研究院 Outline • • • • • • • Overview Preconditions for evolution Deep homology Mechanisms of evolutionary changes Developmental constrains on evolution Selectable epigenetic variation Summary What is Evolution ? What is Evolution ? Evolution is the change in the inherited characteristics of biological populations over successive generations. Evolutionary processes give rise to diversity at every level of biological organization, including species, individual organisms and molecules such as DNA and proteins. What is Evolution ? • Descent from a common ancestor • Natural selection • At the different level Timeline of evolution theory 1735 biological classification 1809 Lamarckism 1858 0n the origin of species 1865 Mendel's laws population genetics 1896 Weismannism “germ cells vs Somatic cells” 1953 DNA structure Galapagos Summary of Darwin’s theory Every species is fertile enough that if all offspring survived to reproduce the population would grow (fact). Despite periodic fluctuations, populations remain roughly the same size (fact). Resources such as food are limited and are relatively stable over time (fact). A struggle for survival ensues (inference). Individuals in a population vary significantly from one another (fact). Much of this variation is inheritable (fact). Individuals less suited to the environment are less likely to survive and less likely to reproduce; individuals more suited to the environment are more likely to survive and more likely to reproduce and leave their inheritable traits to future generations, which produces the process of natural selection (inference). This slowly effected process results in populations changing to adapt to their environments, and ultimately, these variations accumulate over time to form new species (inference). Ernst Mayr Why we need to understand evolution? "nothing in biology makes sense except in the light of evolution" Theodosius Dobzhansky Basics of Biology • Theory of evolution • Mendelian inheritance • The central dogma of molecular biology How “far” away they are How “close” they are How does evolution work • Preconditions for evolution: The developmental structure of genome • Modularity • Molecular parsimony The small tool kit Modularity: Divergence through dissociation Modularity: Divergence through dissociation • Apterous Molecular parsimony: gene duplication and divergence • Some “tool kit” genes play the same roles in all animals • Gene duplication provides opportunities for divergence. • Paralogues • Orthologues Molecular parsimony: gene duplication and divergence Deep Homology Mechanisms of evolutionary change Evolution works with what it has: • • • • Change in location (Heterotopy) Change in time (Heterchrony) Change in amount (Heterometry) Change in kind (Heterotypy) Heterotopy Fgf8 BMP apoptosis Heterotopy Fgf10 attract ribs to enter the dermis BMP induce the bone formation Heterchrony Heterometry • Darwin’s finches Heterometry Heterotypy • Why insects have only six legs? Developmental constraints on Evolution • Physical constraints • Morphogenetic constraints • Phyletic constraints Physical constraints Morphogenetic constraints Phyletic constraints Selectable epigenetic variation: Environment cues • Somatic cells VS germ cells What is wrong with lamarck? • Epialleles • Symbiont variation • Genetic assimilation Epialleles Symbiont variation Interaction with an expected population of symbionts could result in phenotypic plasticity. When symbionts are transmitted through the germ line, the symbionts provide a second system of inheritance. Symbiont variation Genetic assimilation • The environment could both “induce” and “select” a phenotype. • Genetic assimilation happens both in labs and in nature. • Fixation of environment induced phenotypes 1. The phenotype is not random. 2. The phenotype already exists in a large portion of population Summary • Variation-modularity, molecular parsimony, and duplication- enable changes in development without destroy the organism. • Four modes of genetic changes act during development to produce new and large variation in morphology. • Epigenetic inheritance provide selectable variations and aid their propagation through a population.