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Evolution 9.docx

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BIOL 121
Carol Pollock

Evolution 9: Great Changes: Diversity and Divergence Big Changes: 1. Genetic Mechanisms - Homeotic Genes – are very important in development on the axis of growth and required to tell other genes when to start (code for transcription factors) Q. Which of the following observations is consistent with the hypothesis that increasing animal complexity is associated with an increase in the mumber of Hox loci? A. Phyla that branch off early, such as sponges and cnidarians (jellyfish), have simple body plants with relatively few Hox loci. B. Hox loci are similar in structure and DNA sequence and are grouped in clusters. Thus, they are assumed to have arisen through mutation and duplication. When a new Hox gene appears with lineage, most of the descent groups have homogenous Hox locus. C. In vertebrates, it seems that there Hox loci are duplicated multiple times. D. All of the above 2. Adaptive radiation - they produce star phylogenies (single lineages produce many species with diversity of habitats and feeding strategies relatively quickly) – rapid speciation Ex. Hawaiian honeycreepers underwent adaptive radiation – different beak lengths that will now go after different kinds of food and live in different places How? 1. Ecological opportunity = after a disturbance, new species may have the opportunity to come in 2. Morphological Innovations = an adaptive change that happens to be beneficial in their environment. 3. Mass extinctions = species are always becoming extinct Back ground rate = 50,000 species per year. Back ground rate is NOT the same as mass extinction, mass extinction = when LOTS of species die off at once suddenly that is GLOBAL, whereas background extinction = happening locally In the history of the world, there have been 5 big mass extinctions = “The Big 5” - Cambrian explosion = ~40 million years ago - Mammalian diversification = ~65-50 million years ago 1. End Permian (250 millions of years ago) = was the end of ~90% marine species, ~1/3 of terrestrial species - which took 5 million years (this is VERY fast relatively) Not sure what did it = most likely volcanic eruptions due to movements of continentsIncrease in CO2 decrease in O2 = dinosaurs survived  age of the dinosaurces 2. End of the Cretaceous – beginning of the Paleogene (K – Prestinction) End of the dinosaurs Thought to be the cause of a hit by an asteroid, near the gulf of mexico  Primate lineage consists of two main groups: 1. Prosimians 2. Anthropoids What makes humans unique? - bipedalism - opposable thumbs - language - strength and flexibility - extends complexity - brain development - lack of hair - tools - self-consciousness - problem solving ^ These are all “valid” but these characteristics can be found in other species as well, but having ALL these characteristics is what sets us apart Phylogeny of Modern Humans - Common ancestor of all humans alive today - Three monophyletic groups suggest that once humans left easy Africa, the population sp
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