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7A – Evidence of Evolution
Homologies and Analogies
TEK 7A
• 7A analyze and evaluate how evidence of
common ancestry among groups is provided
by the fossil record, biogeography, and
homologies, including anatomical, molecular,
and developmental.
Which two organisms are closely
related to each other?
Shark and Dolphin
Or
Cauliflower & Broccoli
WHY????
Homologous Structures
• traits inherited
by two
different
organisms from
a common
ancestor
• Sometimes
different
function, but
same structure
•How do you know that these four organisms are related?
Although the organisms do not resemble each
other from the outside or even perform the
same functions, on the inside the structure is
the same in the limbs.
Homologous Body Structures
Section 15-3
Turtle
Alligator
Bird
Ancient lobe-finned fish
•Just because they have the same structure does that mean they:
•Look the same on the outside?
•Live in the same habitat?
•Eat the same type of food?
Mammal
Analogous Structures
• Two very different organisms evolve a similar
function or characteristic independently of
one another due to similar environmental
challenges, not common ancestry
• Same function, different structures
Of Shrimp and Snails
analogous or homologous?
Analogous: Inside their shells are very
different:
Barnacles and limpets have many
superficial similarities: both are
small creatures with conical shells
and can be found in the ocean on
rocky shores….so analogous or
homologous?
Which one below has the insides of
a shrimp and which has the insides
of a snail?
• Barnacles
Limpets
So does that mean they had a common
ancestor whose was closely related to
them?
• Who do you
think was the
ancestor of
barnacles and
limpets? Talk
with your
partner (30
sec).
WHY are they not closely
related???
• The common ancestor had no conical shell.
• Similar shells evolved because both lineages
faced a similar challenge:
– a rocky, wave-swept environment teeming with
predators ready to pry a small creature off a rock
for lunch — and conical, hard-to-get-a-grip-on
armor offers a lot of protection in such an
environment. These lineages evolved their shells
independently — meaning that the shells of these
two lineages are analogies.
Analogous or Homologous?
Analogous or Homologous
Analogous or Homologous
Analogous or Homologous:
Jaws vs Flipper
Molecular – Genetics
Similarities in DNA
• DNA and
protein (amino
acid)
sequences
suggest
common
ancestry.
Why grow a tail and then lose it?
HUMAN EMBRYO
_________________
has
a tail at 4 weeks
_________________
Tail disappears at
_________________
about
8 weeks
tail
http://www.suite101.com/files/topics/6234/files/tail_HumanTail.gif
Developmental - Embryology
• Embryonic Structures Of Different Species Show
Significant Similarities
• Embryo – early stages of vertebrate development
19
Vestigial Structures
• Vestigial Structures:
– No useful function
• Ex: hipbones in whales & boa constrictors or
tail & appendix in humans
Vestigial Structures
• What other structures can you think of
that are considered vestigial?
• Turn and talk with your partner: (30 sec)
• What do you think
were some uses of
these now vestigial
structures?
• Remember!!!!
• These structures
were once very
useful.
Cladogram - diagram that shows the
evolutionary relationships among a group of organisms
Concept Attainment Quiz
• Students will fill out graphic organizer
• Teachers see notes below
Complete “Out” for Homework!!!
• Complete packet with your neighbors. DUE
TODAY  - Get busy
• QUIZ NEXT CLASS!!!