Transcript Whippo

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 amphibius
Terrestrial & 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
Ichthyostega
• These fossils are literally half fish, half
•
amphibian
Fossils that show transitions between species
are called “transitional fossils”
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
Common ancestry of organisms
explains many puzzles such as the
distribution of the Hb gene
Hb
Hb
Hb
Hb
Hb
Hb
Hb
Hb
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?
Hemoglobin (again) - how molecular biology
is used to estimate dates of common ancestry
Last
Amino
Comm •
Acid
on
Chang
•
Ancest
es*
or
Human/
5
30 MY
monkey
•
Bird/ma
250
32
mmal
MY
* Changes per 100 codons
Reptile/
320
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!
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
– Their DNA is the same (or
–
nearly so)
Each of their proteins are the
same
• With time, mutations make
Computer alignment:
•
their DNA (and proteins)
different
Computers can align regions
of DNA that did not change
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