Marjorie Angelica Balaguer
Baccalaureate Biology HL 11-1/2
Option D: Evolution
Phylogeny and Systematics I-II (4.22 – 4.30 2010)
Phylogeny and Systematics I
Phylogeny – the study of evolutionary relatedness among various groups of organisms.1 (Common ancestry or
convergent, DNA & genetic similarities)
Systematics – the study of the diversification of life on the planet Earth, both past and present, and the
relationships among living things through time.2
+ Outline the value of classifying organisms
Classifying organisms allows us to;
- Identify unknown organisms
- Determine evolutionary relationships
- Make predictions about members of a group, based on data from another
+ Define clade and cladistics
Clade – (monophyletic group) A common ancestor and all its descendants
Cladistics – A system of natural classification in which organisms are grouped based on characteristics that
they share amongst themselves and a recent common ancestor
+ Distinguish, with examples, between homologous characteristics and analogous characteristics
Homologous characteristics – are characteristics shared by two or more species that are derived from (were
present in) a common ancestor. The structure of homologous characteristics is the same or similar among
organisms, though the function may vary. Examples include the forelimbs of land vertebrates and the
vertebral column of all vertebrates.
Analogous characteristics – are characteristics shared by two or more species due to convergent evolution.
These structures have the same function, but may be structurally different. Examples include insect and fly
wings and the shark and cetacean dorsal fins.
+ Explain the biochemical evidence provided by the university of DNA and protein structures for the
common ancestry of living organisms
 Early ideas about evolutionary relationships were based on anatomical evidence. It is now known that
DNA is the molecule of inheritance used by all organisms and the genetic code is universal. Species
hypothesized to be closely related to one another have more similar DNA sequences to each other.

Protein sequences and structures are also similar among closely related organisms. Taken together,
these biochemical data support the concept of common ancestry.
1.
2.
http://en.wikipedia.org/wiki/Phylogenetics
http://en.wikipedia.org/wiki/Systematics
Marjorie Angelica Balaguer
Baccalaureate Biology HL 11-1/2
+ Explain how variations in specific molecules can indicate phylogeny (relatedness)
Shared sequences of amino acids (proteins) and nucleotides (DNA) as well as the number of
differences among sequences allow determination of relationships among organisms. In order to compare
these data, alignments (comparisons) of sequences must be performed.
For example:
(DNA sequences are taken from both nuclear DNA and mitochondrial DNA)
Species
#1
#2
#3
#4
1
A
A
A
A
2
A
A
A
A
3
A
A
A
C
4
A
A
A
A
5
T
C
C
T
6
T
T
T
C
7
T
T
T
T
8
T
A
A
T
9
C
C
C
C
10
C
C
C
C
11
C
C
C
A
12
C
G
G
C
13
G
G
C
G
14
G
G
G
C
15
G
G
G
T
16
G
G
G
G
Bold & Boxed – differences in sequence
+ Discuss how biochemical variations can be used as an “evolutionary clock”
In addition to determining relationships, differences in DNA sequences can be used to estimate the
amount of time that has passed since the divergence of two species from a common ancestor.
However, because rates in mutation and evolution are not constant, there is some uncertainty (+/- x
years) involved in determining divergence times.
1.
2.
http://en.wikipedia.org/wiki/Phylogenetics
http://en.wikipedia.org/wiki/Systematics
Marjorie Angelica Balaguer
Baccalaureate Biology HL 11-1/2
Phylogeny and Systematics II
+ Outline the methods used to construct cladograms and the conclusions that can be drawn from them.
1. Make a list of all of the organisms included in the study
2. List the characteristics included in the study
3. Make a table with the characteristics in the heading columns and the taxa (Kingdom, Phylum, Class,
Order, Family, Genus or Species) in the rows.
4. Order characteristics left to right from the most widely shared characteristic to the lease widely
shared.
5. Order the taxa top to bottom so the organism with the fewest traits is at the top, most at the bottom.
*** The cladogram graphically illustrates the taxa organized in terms of shared characteristics derived from
recent ancestors.
+ Sample cladogram: (2 step process)
Step 1:
Table and arrangement of taxa and characteristics
*Table below is already ordered from least to greatest – it may not come out this way when observing real data
or other information.
Taxa
Lamprey
Sunfish
Newt
Lizard
Bear
Chimpanzee
Human
Backbone
Jaw
Forelimbs
1
1
1
1
1
1
1
0
1
1
1
1
1
1
0
0
1
1
1
1
1
KEY
1 – Yes, organism has characteristic
0 – No, organism does not have characteristic present
1.
2.
http://en.wikipedia.org/wiki/Phylogenetics
http://en.wikipedia.org/wiki/Systematics
Amniotic
Egg
0
0
0
1
1
1
1
Mamary
Glands
0
0
0
0
1
1
1
Opposable
Thumbs
0
0
0
0
0
1
1
Upright
Posture
0
0
0
0
0
0
1
Marjorie Angelica Balaguer
Baccalaureate Biology HL 11-1/2
Step 2:
Cladogram with arrangement of taxa and characteristics
Lamprey
Sunfish
Newt
Lizard
Bear
Chimp
Human
Upright Posture
Opposable Thumbs
Mammary Glands
Amniotic Egg
Forelimbs
Jaw
+ Discuss the relationship between cladograms and the classification of living organisms
Cladograms are organized such that taxa are grouped based on evidence of relationships. Each
derived characteristic that is added to a data set helps define a particular group (ex: hair defines mamalia)
The Linnaean system of classification that provided names for many groups does not operate based on
evidence for relationships, thus cladistics is now widely used for classification.
1.
2.
http://en.wikipedia.org/wiki/Phylogenetics
http://en.wikipedia.org/wiki/Systematics