Presentation on theme: "Introductory Biology in-class interactive lecture on evolution."— Presentation transcript:
1Introductory Biology in-class interactive lecture on evolution.
2We will use an attribute table to make a phylogenetic tree based on 3 lines of evidence Observations of habitat and eating habitsObservations of skeletonsObservations of gene sequencesAfter each observation we will modify our tree
11Now draw a tree similar to this example based on diet & habitat
12Skeletal evidenceSkeletons provide strong evidence that all vertebrates share a common ancestrySkeletal evidence comes from species that are now living and from fossils of species that have become extinct
13Several fossil discoveries show how amphibians descended from fish IchthyostegaThese fossils are literally half fish, half amphibianFossils that show transitions between species are called “transitional fossils”
14Fossil record also clearly shows the reptile to mammal transition Examples of features that are part reptilian and part mammalian:Jaw jointToothRibs on neck vertebraeLycaenops -- a carnivorous therapsid
15Vestigial bones also provide more evidence of common ancestry among vertebrates Pelvic girdle in some snakes, tailbone in humansRemnants of structures with important functions in ancestors but no longer used
16Vestigial pelvic bones in whales -- did their ancestors have legs?
17Homologous structures in mammal skeletons demonstrates common ancestry Features, like the bones of mammals, are said to be homologous, because they share a common structural patternConclusion: all mammals are derived from a common ancestor
25Now draw a tree similar to this example based skeletal features
26Molecular biology evidence A common genetic code for all living things is evidence that all are relatedComparison of DNA among living organisms has strengthened and clarified our understanding of evolutionary relationships
27% Genes from other organisms that also occur in H % Genes from other organisms that also occur in H. sapiens: deep genetic homologiesMouse - 86%* Fruit fly - 44%Nematode worm - 25% Yeast - 30%Amoeba - 22% Mustard (plant) - 19%E. coli (bacterium) - 9% *Of those genes now identified in mice, 86% of them also occur humansThese numbers will change as their genomes are more fully know.
28Common ancestry of organisms explains many puzzles such as the distribution of the Hb gene Because it was present in a common ancestor billions of years ago!Puzzle posed earlier: The hemoglobin gene is widely distributed throughout living organisms. Why?
29Hemoglobin (again) - how molecular biology is used to estimate dates of common ancestry Amino Acid Changes*Last Common AncestorHuman/monkey530 MYBird/mammal32250 MYReptile/Amphibian49320 MYAmphibian/Fish50400 MYAll vertebrates have genes that make hemoglobinLike many other genes, hemoglobin genes mutates at a fairly constant rate, even if they are in different animal groupsRate of change can be used to estimate how long ago groups or organisms diverged from one another!* Changes per 100 codons
30Using molecular biology evidence to draw phylogenetic trees Evolutionary relationships are reflected in the similarity of DNA and proteins among speciesThe closer the match between sequences, the more recent the common ancestor
31Closely related species have similar DNA (and proteins) Closely related species have similar DNA (and proteins). Similarity reflects ancestry.
32Two related species start with similar DNA, but mutations occur, making their DNA different Assume species A & B just arose from the same common ancestorThere DNA is the same (or nearly so)Each of their proteins are the sameWith time mutations make their DNA (and proteins) differentComputers can align regions of DNA that did not changeComputer alignment:
33Computers build phylogenetic trees based on sequence data
38About the hippo-whale relationship DNA data suggested hippos as whale’s closest land relative but there was no fossil evidence to support this theoryRecent discovery of 47 million year old fossils from a proto-whale provided fossil evidence -- hippo’s and whales are closely relatedKey fossil evidence -- the hippo has a distinctive ankle bone and so does the proto-whale!
39Recent discoveries of transitional fossils show that whale ancestors did have legs Ambulocetus(the walking whale)Carl Dennis Buell