Bio SC 1010 1st Edition Lecture 17Outline of Last Lecture I. TaxonomyII. Species Outline of Current Lecture I. Evolutionary Relationships may be represented by branching treesII. Clades van be thought of representing a branch on the tree of lifeIII. New SpeciesIV. HomologyV. DNA sequencesVI. Descent with ModificationVII. Fossil RecordVIII. Radiometric DatingCurrent LectureEvolutionary Relationships may be represented by branching trees • Phylogenetic trees reflect the evolutionary history of organisms• Present a hypothesis about the evolutionary historyClades van be thought of representing a branch on the tree of life• A clade is any group of species that consists of an ancestral species and all its descendants• The TIPS of the tree represent groups of extant (living) species• To determine how closely related two species are, find their most recent common ancestor (NODE)• We start with descriptions and then group by shared derived (new) traits• In a phylogenetic tree the tips indicate organisms• If a branch ends short that indicated that the organism is no longer living• The other organisms are all extant (currently living)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.• Phylogenetic trees can be represented in many different ways, square or triangular• The tips can rotate at each node• Each of the three trees in the blue box are identical• Each node represents the most recent common ancestor between two organismsNew Species• New species may form over long periods of time• In the graduated model, a species acquires small adaptations to its environment over millions of years • New species may form relatively rapidly • In the punctuated equilibrium model, there are periods of stasis interrupted by occasional bursts of speciation-530 million years ago during a period called the Cambrian explosion-the rate of evolution was an order of magnitude higher than the normal rate. (It still required millions of years)Homology• Related organisms share DNA sequences inherited from a common ancestor• Over time, the sequence in each species acquire independent mutations • The more time that has passed, the greater the number of sequence differences that willbe present • Closely related species will have fewer DNA sequence differences that species that are more distantly related • A similarity due to common ancestry• All tetrapod’s share the same forelimb bones-arranged in the same order • Mutations can produce subtle changes I the DNA that cods for proteins• Diverse organisms sharing homologous structures and put them to different uses • Homology is also see in early development• HOX genes-a group of genes that control the body plan on the embryo (legs, antennae, wings of fruit flies, ribs of humans)-determine segment structures-anterior posterior (head to tail)• Similar embryological structures are evidence that all vertebrates shared a common ancestor• Vestigial structure is a structure inherited from an ancestor that no longer serves a clear function in the organism that possesses itDNA sequences• They can tell us:-which extant organisms are the direct ancestors of modern humans-exactly how evolution occurred-approximately how long ago two species diverged-how humans evolved first from monkeys Descent with Modification• Darwin’s term • Combines the ideas-all living things are related-organisms have changed over timeFossil Record• The fossil record supports Darwin’s theory• The fossil record shows an ordered succession of evolutionary stages• Organisms evolved and diversified• Prokaryotes appear before eukaryotes-single cell organisms before multicellular ones-water dwelling organisms before land dwelling• The fossil record: assemblage of fossils arranged in order of age-provides evidence of changes in species over time• Paleontologists are scientists who study ancient life by means of the fossil record • Fossils are preserved remains or impressions of once-living organisms• Fossils form only in certain circumstances• Not a completed record• Supplied an impressive body of evidence for evolution• The fossil record provides important evidence for evolution• Fossils form when organisms die, fall into accumulating sediment, and are compressed into rock • Not every organism that dies forms a fossil• Bony skeletons or hard shells are more likely to fossilize• Organism must be covered quickly upon death or create an imprint in special types of sediment• Fossils are at least as old as the rocks that encase them• Rocks maybe dated directly using radiometric dating• Fossils are at least as old as the rocks that encase them• Rocks maybe dated directly using radiometric dating• Relative dating determines the age of the fossil from its positionRadiometric Dating• Radiometric dating uses radioactive isotopes-an element decays into another element by emitting energetic particles (radiation)-this happens at a known rate (speed)• Determine how much is lost as a measure of age for that rock or