Introductory biology in class interactive lecture on evolution
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Introductory Biology in-class interactive lecture on evolution. We will use an attribute table to make a phylogenetic tree based on 3 lines of evidence. Observations of habitat and eating habits Observations of skeletons Observations of gene sequences

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Introductory Biology in-class interactive lecture on evolution.

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Introductory Biology in-class interactive lecture on evolution.


We will use an attribute table to make a phylogenetic tree based on 3 lines of evidence

  • Observations of habitat and eating habits

  • Observations of skeletons

  • Observations of gene sequences

  • After each observation we will modify our tree


Black bear (Ursus americanus)Terrestrial Omnivore


Harp Seal (Phoca groenlandica)


Harp Seal (Phoca groenlandica)Aquatic & Terrestrial, Carnivore


Hippopotamus amphibiusTerrestrial & Aquatic, Herbivore


Sea Otter (Enhydra lutris)Aquatic, Carnivore


King Penguin (Aptenodytes patagonicus)Aquatic & Terrestrial, Carnivore


Harbor Porpoise (Phocoena phocoena)Aquatic, Carnivore


Blue Whale (Balaenoptera musculus)Aquatic, Omnivore


Now draw a tree similar to this example based on diet & habitat


Skeletal evidence

  • Skeletons provide strong evidence that all vertebrates share a common ancestry

  • Skeletal evidence comes from species that are now living and from fossils of species that have become extinct


Several fossil discoveries show how amphibians descended from fish

  • These fossils are literally half fish, half amphibian

  • Fossils that show transitions between species are called “transitional fossils”

Ichthyostega


Fossil record also clearly shows the reptile to mammal transition

  • Examples of features that are part reptilian and part mammalian:

    • Jaw joint

    • Tooth

    • Ribs on neck vertebrae

Lycaenops -- a carnivorous therapsid


Vestigial bones also provide more evidence of common ancestry among vertebrates

  • Pelvic girdle in some snakes, tailbone in humans

  • Remnants of structures with important functions in ancestors but no longer used


Vestigial pelvic bones in whales -- did their ancestors have legs?


Homologous structures in mammal skeletons demonstrates common ancestry

  • Features, like the bones of mammals, are said to be homologous, because they share a common structural pattern

  • Conclusion: all mammals are derived from a common ancestor


Bear


Seal skeleton


Hippopotamus


Sea otter


Penguin


Porpoise


Whale


Now draw a tree similar to this example based skeletal features


Molecular biology evidence

  • A common genetic code for all living things is evidence that all are related

  • Comparison of DNA among living organisms has strengthened and clarified our understanding of evolutionary relationships


% Genes from other organisms that also occur in H. sapiens: deep genetic homologies

  • Mouse - 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 humans


Because it was present in a common ancestor billions of years ago!

Hb

Common ancestry of organisms explains many puzzles such as the distribution of the Hb gene

Hb

Hb

  • Puzzle posed earlier: The hemoglobin gene is widely distributed throughout living organisms. Why?

Hb

Hb

Hb

Hb

Hb


Hemoglobin (again) - how molecular biology is used to estimate dates of common ancestry

  • All vertebrates have genes that make hemoglobin

  • Like many other genes, hemoglobin genes mutates at a fairly constant rate, even if they are in different animal groups

  • Rate of change can be used to estimate how long ago groups or organisms diverged from one another!

* Changes per 100 codons


Using molecular biology evidence to draw phylogenetic trees

  • Evolutionary relationships are reflected in the similarity of DNA and proteins among species

  • The closer the match between sequences, the more recent the common ancestor


Closely related species have similar DNA (and proteins). Similarity reflects ancestry.


Two related species start with similar DNA, but mutations occur, making their DNA different

  • Assume species A & B just arose from the same common ancestor

    • There DNA is the same (or nearly so)

    • Each of their proteins are the same

  • With time mutations make their DNA (and proteins) different

  • Computers can align regions of DNA that did not change

Computer alignment:


Computers build phylogenetic trees based on sequence data


A portion of the aligned sequences


Part of the aligned DNA sequences


Now draw a tree similar to this example based on DNA sequence data


Phylogenetic tree from DNA data


About the hippo-whale relationship

  • DNA data suggested hippos as whale’s closest land relative but there was no fossil evidence to support this theory

  • Recent discovery of 47 million year old fossils from a proto-whale provided fossil evidence -- hippo’s and whales are closely related

  • Key fossil evidence -- the hippo has a distinctive ankle bone and so does the proto-whale!


Recent discoveries of transitional fossils show that whale ancestors did have legs

Ambulocetus

(the walking whale)

Carl Dennis Buell


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