Download Introduction into Phylogenetics I Introduction: A. Phylogenies depict

Introduction into Phylogenetics
I
Introduction:
A. Phylogenies depict evolutionary relationships by grouping organisms according to
shared derived characteristic traits that are evolutionarily unique among a
particular group of organisms.
1. Example: All mammals have hair
2. Example: We can also group organisms by DNA sequences
(a) ATGTCCTAGG
(b) ATGTCCAAGG closely related to (a)
(c) AGCTAAGCCC  not closely related to (a)
B. Phylogenetic Trees
1. Describe evolutionary history by illustrating the patterns of relatedness among
different groups of species
2. •Closely related groups thought to share a recent common ancestor will occupy
branches closer to each other
3. In the below Phylogenetic Tree, Conifers and Flowering Plants are more closely
related than Mosses and Flowering Plants
4. Each branch on a Phylogenetic Tree represents the divergence of two groups
from a common ancestor.
C. Three Classifications of Species in Phylogenetic Trees
1. Monophyletic Groups – Include all descendents of a single common ancestor –
AKA clades
2. Paraphyletic Groups – Include some, but not all, descendents of a single common
ancestor
3. Polyphyletic Groups – Include descendents, but not the common ancestor, of all
species in the group.
D. Some important vocabulary terms to know:
1. Homoplasy – shared characteristics not inherited from a common ancestor –
creates conflict for biologists
(a) Example: sharks and tigers both have tails, but they do not share an ancestor
2. Convergent Evolution – Occurs when distantly related organisms face similar
environmental challenges and evolve to have similar traits
3. Analogous – traits that are similar due to convergent evolution
4. Homologous – traits that are similar due to a common ancestry
E. When building a Cladogram, use the Principle of Parsimony (the hypothesis that
makes the least number of assumptions) (KISS – Keep It Simple, Stupid)
F.
This picture comes from chapter 23, the frog does not have a tail so on the right side
we place it next to the gorilla, who also does not have a tail. But if we do this, we are
making 5 assumptions of gained or lost characteristics.
G. If we put the frog next to the salamander and lizard, we only have to make 4
assumptions, which is more simple, so we go with the left Phylogenetic tree.
II Phylogenetic Trees
A. Reading Them
1. They come in different forms, but can all be read similarly
2. Species placed closer together are more closely related no matter the orientation
of the tree itself
3. Be careful to determine where time is a long time ago, and where it is at present
time.
B. Remember, Phylogenetic trees depict the current hypothesis of evolutionary
relationships. As we discover more fossils, more DNA data, more evidence of the
evolutionary process, we can change and adapt our trees to reflect this data.
III Classification
A. Classification – how we place species and higher groups
B. Nomenclature – naming that uses two words to name a species.
1. The first word is the Genus
2. The two words together is the Species
3. Example: Homo sapien (Species name for humans, Homo is genus classification)
C. Order:
1. Kingdom
2. Phylum
3. Class
4. Order
5. Family
6. Genus
7. Species
D. Can remember the order of classification with these handy phrases:
1. King Phil Came Over For Good Soup
2. Kings Play Chess On Funny Green Squares
E. Nomenclature is like a funnel, as you move down the list, we get more specific.
1. A lot of species fit a Phylum and Class
2. Only One species is given its species name
F. Classification for Humans:
Category
Human
Classification
Domain
Eukaryote
Kingdom
Animilia
Phylum
Chordata
Class
Mammila
Order
Primates
Family
Hominidae
Genus
Homo
Species
Homo Sapien
1.