The document discusses using molecular evidence like amino acid sequences to determine evolutionary relationships. It provides cytochrome c, a protein found in mitochondria, as an example. Comparisons of cytochrome c amino acid sequences among different organisms can infer how closely or distantly they are related on an evolutionary timescale. The more similar the sequences are, the more closely related the organisms. The document emphasizes that using multiple lines of molecular evidence provides stronger inferences about evolutionary relationships than any single source alone.

2. Topic Outline
A recognize how comparisons of similarities and differences
can suggest evolutionary relationships
B explain the significance of using multiple lines of
evidence to identify evolutionary relationships
C infer the degree of relationships among organisms
based on the amino acid sequence in the cytochrome c
molecule

3. • All life on Earth arose from a single common ancestor, and our genes reflect this
shared ancestry. As species differentiated over evolutionary time, the DNA
sequences in their genes acquired slight changes. According to evolutionary theory,
these changes accumulate over time: species that diverged from each other long
ago have more differences in their DNA than species that diverged recently.

4. • Living things share some biomolecules which may be used to prove relationships. These
chemicals include DNA and proteins. The building blocks of these chemicals may be analyzed
to show similarities and differences among organisms. The more similarities, the closer the
relationships.

5. Molecular Comparisons
• With the advancement of DNA technology, the area of molecular
systematics, which describes the use of information on the molecular
level including DNA sequencing, has blossomed. New analysis of
molecular characters not only confirms many earlier classifications,
but also uncovers previously made errors. Molecular characters can
include differences in the amino-acid sequence of a protein,
differences in the individual nucleotide sequence of a gene, or
differences in the arrangements of genes.

6. • One example that supports the molecular
evolutionary relationships is the basis from the
protein cytochrome-c, an important enzyme
found in virtually all organisms. It is a highly
conserved protein which functions in the electron
transport chain system of the mitochondria which
is needed for the release of energy from food.
The Molecular mitochondria which is needed for
the release of energy from food. It also performs a
role in apoptosis (programmed cell death) by
being released into the cytosol activating the
events of cell death. The diagram below shows the
structure of cytochrome c and its location in the
mitochondrial inner membrane

10. • Two Options for Similarities
• In general, organisms that share similar physical features and genomes tend to be
more closely related than those that do not. Such features that overlap both
morphologically (in form) and genetically are referred to as homologous structures;
they stem from developmental similarities that are based on evolution. For example,
the bones in the wings of bats and birds have homologous structures.
• Notice it is not simply a single bone, but
rather a grouping of several bones
arranged in a similar way. The more
complex the feature, the more likely
any kind of overlap is due to a common
evolutionary past.

11. • Some organisms may be very closely related, even
though a minor genetic change caused a major
morphological difference to make them look quite
different. Similarly, unrelated organisms may be distantly
related, but appear very much alike. This usually happens
because both organisms share common adaptations that
evolved within similar environmental conditions. For
example, insects use wings to fly like bats and birds, but
the wing structure and embryonic origin is completely
different. These are called analogous structures

12. HOMOLOGOUS STRUCTURES
• similar physical features in organisms
that share a common ancestor, but
the features serve completely
different functions.
ANALOGOUS STRUCTURES
• features of different species that are
similar in function but not necessarily in
structure and which do not derive from a
common ancestral feature

13. EVOLUTION IN ACTION:
What is Phylogeny and Why Does It Matter?
• Phylogeny is the study of relationships among different groups of
organisms and their evolutionary development. Phylogeny attempts
to trace the evolutionary history of all life on the planet. It is based on
the phylogenetic hypothesis that all living organisms share a common
ancestry.

14. Building Phylogenetic Trees
• How do scientists construct phylogenetic trees? Presently,
the most accepted method for constructing phylogenetic
trees is a method called cladistics. This method sorts
organisms into clades, groups of organisms that are most
closely related to each other and the ancestor from which
they descended.

15. • Clades can vary in size depending on
which branch point is being referenced.
The important factor is that all of the
organisms in the clade or monophyletic
group stem from a single point on the
tree. This can be remembered because
monophyletic breaks down into “mono,”
meaning one, and “phyletic,” meaning
evolutionary relationship. The figure
below shows various examples of clades.
Notice how each clade comes from a
single point, whereas the non-clade
groups show branches that do not share
a single point.

16. To make the Cladogram, we must observe which characteristics are more or
less commonly held

17. Through this cladogram, we can conclude that among the organisms crocodiles and
birds are the most closely related, while butterflies are the outgroup

18. cells
legs
6 legs
wings
worms spider
carpenter ant
(black)
fly

19. cells present present present present
legs absent present present present
6 legs absent absent present present
wings absent absent absent present
worms spider
carpenter ant
(black)
fly

20. • To build phylogenetic trees, scientists must collect character
information that allows them to make evolutionary connections
between organisms. Using morphologic and molecular data,
scientists work to identify homologous characteristics and genes.
Similarities between organisms can stem either from shared
evolutionary history (homologies) or from separate evolutionary
paths (analogies). After homologous information is identified,
scientists use cladistics to organize these events as a means to
determine an evolutionary timeline. Scientists apply the concept of
maximum parsimony, which states that the likeliest order of events is
probably the simplest shortest path. For evolutionary events, this
would be the path with the least number of major divergences that
correlate with the evidence.
Section Summary

21. Thank you for
listening!
Don't hesitate to ask any questions!

22. ACTIVITY
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