Download Homologous structures

Homologous structures
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Structures on different organisms are
homologous when they have similar
base structures but have different
functions.
Homologous structures
Human Arm
Bat Wing
Whale Flipper
Analogous Structures
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Similar functions but NOT
structurally related.
Insects are arthropods and birds
are vertebrates.
The wing of a bird and the wing
of a butterfly are examples of
analogous structures.
Comparative embryology
Vestigial Structures
A structure in an organism that has
lost all or most of its original
function
Transition fossils
The Panda's Thumb
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A classic example of evolution.
The giant panda is a bear that
adapted to eating bamboo.
The panda’s opposable thumb
Giant pandas have a thumb
pad on the hand
This thumb pad is used by
the panda to grasp bamboo
shoots
It uses its thumb to hold and
manipulate the bamboo while
eating
The Panda has not always had this opposable
thumb. Fossil evidence shows that this has
evolved over thousands of years.
Comparing bones.
Unrelated species evolve similar traits
even though they live in different parts of
the world, or at different times in Earth’s
history
Analogous Structures = Convergent
Evolution
Analogous
Structures =
Convergent
Evolution
Analogous
Structures =
Convergent
Evolution
Divergent Evolution: one species
gives rise to many species
Divergent Evolution
 One species gives rise to many
species in response to the creation
of new habitat or other ecological
opportunity
 Gives rise to homologous
structures
Geographic isolation: prevents
individuals of a species in different
populations from mating
Geographic isolation prevents a mix of genes with
the original species.
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Example: Kodiak Brown Bears
This group of bears have
evolved into a sub-species,
that is different form all other
grizzly bears.
An archipelago is a landform which
consists of a chain or cluster of islands.
Adaptive
radiation:

many species
appear to be
related to a
single
ancestral
species.
Reproductive Isolation: prevents individuals
from reproducing with each other
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Prezygotic isolating mechanisms :
prevent reproduction before fertilization
Postzygotic isolating mechanisms:
prevent reproduction after fertilization
GRADUALISM
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Living things change very slowly in small,
gradual steps: GRADUALISM
PUNCTUATED EQUILIBRIUM
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Sometimes species will remain the same for a
long period of time and then change very
quickly.
This is usually the result of some
catastrophic disaster like an earthquake or
volcano.
GALAPAGOS FINCHES
THE EVOLUTION OF BEAK SHAPE IN
GALAPAGOS FINCHES
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Darwin first thought about evolution while
studying in the Galapagos
13 species of finches in the Galapagos islands
Islands are barriers that separate each group of
the species- “Geographic Isolation”
size and shape of the beak has an important
consequence for fitness. (What is Fitness?)
Darwin’s finches
Medium Tree
Finch
Cactus Ground
Finch
Medium
Ground
Finch
Warbler
Finch
GALAPAGOS FINCHES
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Each species has a highly characteristic beak shape.
Darwin focused his study on the link between the shape
of the beak, the food and the habitat of each species.
This research of his was to result in the theory of
evolution and the 14 finches became "stars" in their own
right.
The Case of the Galapagos Finches
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All species of finch derive from the same original species.
The observation: despite their strong resemblance, each
species of finch has a highly characteristic beak shape.
The evolutionary factors: geographic isolation, ecological
environment, food sources, competition.