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Welcome
Topic
Banking
Management SystemParsimony Method for
Phylogenic Tree Analysis
Presented By
Anika OhabID:142-15-3568
Abul HasnathID:142-15-3532
Umme HabibaID: 142-15-3677
Shahinur Rahman ID: 142-15-3606
Introduction
kinds
terminology
construction
Parsimony method
advantage
disadvantage
Several criteria
Contents
IntroductionA phylogenetic tree or evolutionary tree is a
branching diagram or "tree’’showing the inferred evolutionary relationships among various biological species
or other entities—their phylogeny—based upon
similarities and differences in their physical or genetic characteristics.
Phylogenetic trees are central to the field of phylogenetics.
What does this tree look like?There are many different ways to represent the
information found in a phylogenetic tree. The basic format of a tree is generally in one of the
two forms shown, although there are other ways to represent the data.
phylogenetic tree
Rooted Unrooted
Kinds
“Rooted” &“Unrooted” treeA rooted tree is used to make inferences about
the most common ancestor of the leaves or branches of the tree. Most commonly the root is referred to as an “outgroup”.
An unrooted tree is used to make an illustration about the leaves or branches, but not make assumption regarding a common ancestor.
The bifurcating treeA tree that bifurcates has a maximum of 2
descendants arising from each of the interior nodes.
Diagram:
C o
n s t r
u c t I o n
Computational Phylogenetics Methods
Distance-matrix Methods
Neighbor-joining or UPGMA
maximum likelihood
Parsimony Methods
Parsimony analysisParsimony methods provide one way of choosing
among alternative phylogenetic hypotheses
The parsimony criterion favours hypotheses that maximise congruence and minimise homoplasy
It depends on the idea of the fit of a character to a tree
Character Fit Initially, we can define the fit of a character to a
tree as the minimum number of steps required to explain the observed distribution of character states among taxa
This is determined by parsimonious character optimization
Characters differ in their fit to different trees
Frog
Coc
odile
Bird
Kan
gero
o
Bat
Hum
an
Hairabsentpresent
Frog
Kan
gero
o
Coc
odile
Hum
an
Bat
Bird
Tree A1 step
Tree B2 steps
Character Fit
Parsimony AnalysisGiven a set of characters, such as aligned
sequences
parsimony analysis works by determining the fit (number of steps) of each character on a given tree
Most parsimonious trees (MPTs) have the minimum tree length needed to explain the observed distributions of all the characters
Frog
Bird
Crocodile
Kangeroo
Bat
Human
amni
on
hair
win
gs
anto
rbita
l fe
nest
ra
plac
enta
lact
atio
n
Tree 1
Tree 2
T A
X A
FIT
-
-
-
-
--
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
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+
-
+ -
+
-
CHARACTERS
1 2 3 4 5 6
+
+
+
+
1
1
TREE LENGTH
1 1 1 1 2 7
2 2 2 2 1 10
Frog
Coc
odile
Kan
gero
o
Bat Bird
Hum
an
1
23
6
44
5
52
3
Tree 2
Coc
odile
Kan
gero
o
Frog
Bird Bat Hum
an
1
Tree 1
23
4
66
5
Of these two trees, Tree 1 has the shortest length and is the most parsimoniousBoth trees require some homoplasy (extra steps)
Results of parsimony analysisOne or more most parsimonious trees
Hypotheses of character evolution associated with each tree lengths
Various tree and character statistics describing the fit between tree and data
Suboptimal trees - optional
Tree-building methods can be assessed on the basis of several criteria:
Efficiency Power
consistency
robustness
falsifiability
Parsimony - advantagesIt’s a simple method - easily understood operation
Its does not seem to depend on an explicit model of evolution
gives both trees and associated hypotheses of character evolution
good statistical properties when amounts of change aresmall
Parsimony - disadvantagesmay lead to the delusion that you know
exactly whathappened in evolution, in detail.Underestimates branch lengths
Model of evolution is implicit - behaviour of method not well understood
not model-based so people think it makes noassumptions
The End
Thank You
