Chapters 25 and 26. Searching for Homology. Phylogeny

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1 Chapters 25 and 26 The Origin of Life as we know it. Phylogeny traces evolutionary history of taxa Systematics- analyzes relationships (modern and past) of organisms Figure 25.1 A gallery of fossils The fossil record can be used to trace evolutionary relationships between organisms of the past and those of the present Searching for Homology Morphological and molecular similarities among living organisms Organisms similar in appearance also are often similar in molecular make-up (DNA and thus protein sequences) WHEN IS THIS NOT TRUE? Figure 25.5 Convergent evolution of analogous burrowing characteristics Figure 25.6 Aligning segments of DNA 1 Ancestral homologous DNA segments are identical as species 1 and species 2 begin to diverge from their common ancestor. 1 C C A T C A G A G T C C 2 C C A T C A G A G T C C Deletion 2 Deletion and insertion mutations shift what had been matching sequences in the two species. 1 C C A T C A G A G T C C 2 C C A T C A G A G T C C G T A Insertion Marsupial Australian mole 3 Homologous regions (yellow) do not all align because of these mutations. 1 C C A T C A A G T C C 2 C C A T G T A C A G A G T C C Eutherian North American Mole 4 Homologous regions realign after a computer program adds gaps in sequence 1. 1 C C A T C A A G T C C 2 C C A T G T A C A G A G T C C 1

2 Phylogenetic Systematics Taxonomy is the science of naming and classifying life Relies on Binomial nomenclature in which each organism (Species) is given a unique name that includes: Genus Specific epithet Homo sapiens vs. Homo erectus Kings Play Chess On Fine Glass Stools Figure 25.7 Hierarchical classification Figure 25.8 The connection between classification and phylogeny Phylogenetic trees show evolutionary relationships that also reflect hierarchical classification Clade Monophyletic Derived Characters Primitive Characters Monophyly ancestor and all of its descendents Paraphyly group includes ancestor and some of its descendents Polyphyly- multiple groups lack a common ancestor 2

3 Figure Constructing a cladogram Ingroup Outgroup Parsimony Phylograms reflect the numbers of changes that have taken place in a particular gene sequence. Branch length is correlated with differences Ultrametric Trees Place data in context of geologic time Homology vs. Analogy in constructing trees Cladistics is changing the way we classify organisms 3

4 Table 25.1 The Geologic Time Scale The history of life Chapter 26 Figure 26.0 A painting of early Earth showing volcanic activity and photosynthetic prokaryotes in dense mats Miller and Urey Experiments demonstrate how atmospheric conditions could have favored the start of life. 4

5 Figure A window to early life? Figure Laboratory versions of protobionts Figure Abiotic replication of RNA RNA was the first genetic material Ribozymes Ribozymes are used to synthesize trna,, mrna, rrna (a) RNA forms Nucleotides RNA (b) Ribozymes catalyze RNA replication (c) RNA catalyzes protein synthesis Amino acids Protein (d) RNA encodes both DNA and proteins DNA Protein (e) Proteins catalyze cell activities Plasma DNA membrane RNA Protein Bacterial cell Q: Why do you think RNA arose before DNA? Hint: what limitations does DNA have structurally? RNA is autocatalytic, DNA is not RNA molecules can take on many conformations, DNA is limited to double stranded helix RNA can be used to synthesize proteins Why is DNA the primary genetic material today?? 5

6 Sedimentary deposit Figure 25.2 Radiometric dating Relative dating- comparing layers in sedimentary layer at different sites to get time frames Radiometric dating allows us to get absolute dates based upon relative abundances of radioactive isotopes. Figure 25.5 Diversity of life and periods of mass extinction Five major extinctions 440 MYA, late Ordovician - global cooling 365 MYA, late Devonian - global cooling and anoxia of seas, 245 MYA, End of Permian % of marine species went extinct, sustained cooling 210 MYA, End of Triassic - possibly related to increased rainfall - 65 MYA - KT (Cretaceous-Tertiary) % of marine species went extinct, end of the dinosaurs, likely due to large impact event Figure 25.6 Trauma for planet Earth and its Cretaceous life Volcanic activity and lightning associated with the birth of the island of Surtsey near Iceland; terrestrial life began colonizing Surtsey soon after its birth 6

7 3.5 billion years ago First evidence of life appears Oldest fossils are from Australia Stromatolites Prokaryotes dominated evolutionary history until 2.0 billion years ago Figure 26.3 Early (left) and modern (right) prokaryotes Figure 26.4 Bacterial mats and stromatolites Bacterial mats in Baja California Top: Mat from Baja Bottom: Stromatolite from Australia 3.5 billion years old Figure 26.4x Stromatolites in Northern Canada Figure A window to early life? 7

8 2.7 billion years ago Figure 26.5 Banded iron formations are evidence of the vintage of oxygenic photosynthesis oxygen starts to accumulate Photosynthesis that involves the splitting of water evolves: produces lots of O 2 CO 2 and 6 H energy C 6 H 12 O O 2 Q. What would be the selective advantage to adapting to the new O 2 environment??? A. Anaerobic vs. aerobic metabolism!!! Just think of all that ATP!!!!! 2.1 Billion years ago Eukaryotes arise Endosymbiosis Membrane infolding (a) Progenitor of eukaryotes Plasma membrane DNA (c) Ancient eukaryote Mitochondrion Nulear envelope Endoplasmic membrane (d) Eukaryotic protist, fungus, and animal cells (e) Eukaryotic plant cell (b) Proto-eukaryote Cell wall Chloroplast Invagination of cell membrane Future nuclear envelope Mitochondrion Protosynthetic prokaryote Bacterium 8

9 Lines of evidence Size of modern and fossil bacteria Divide by a process similar to binary fission Inner membranes are similar to those found in modern day prokaryotes Have their own genomes, ribosomes, trnas and proteins SSU-rRNA comparisons 1.2 Billion years ago Multicellularity arises Fossilized alga about 1.2 billion years old Fossilized animal embryos from Chinese sediments 570 million years old Multicellular life may have evolved from colonial protists Multicellularity evolved independently many times Probably by specialization of the cells of colonial protists Gamete 1 2 Locomotor cells 3 Somatic cells Foodsynthesizing cells Unicellular protist Colony Early multicellular organism with specialized, interdependent cells Later organism that produces gametes Cambrian period ( mya) Animal diversity EXPLODES!!! Almost all major phyla of animals appear including Cnidarians and Poriferans (jellies and sponges) 9

10 500 mya Plants arrive on land (FINALLY) Plants, fungi and animals all colonize the land Major event in shaping terrestrial life as we know it today. Age of mammals Age of reptiles midnight Insects and amphibians invade the land Plants invade the land First fossil record of animals Plants begin invading noon land Evolution and expansion of life Modern humans (Homo sapiens) appear about 2 seconds before midnight Recorded human history begins 1/4 second before midnight Origin of life ( billion years ago) The tree of life 10