Parsimony

1
Parsimony

• Every possible tree evaluated in terms of total
  number of steps needed to convert each sequence
  to another
• Practical for only a few sequences
• High percentage of similarity a prerequisite
• Neither identical or completely different
  sequence positions useful
• Each difference should represent a single step
  and not a full circle or non-shortest route

2
Parsimony

• ACCEFAHIK LKNPR
• ACCEFGHIL LLNPR
• ACDEFGHIK LINPK
• AADEFGHIL LNNPK
• I II III

No. of possible trees for 4 Sequences 3 (1,2)
(3,4) (1,3) (2,4) (1,4) (2,3) No. of positions
to be considered for each tree 3
1 C
3 D
D
C
2 C
4 D
Candidate tree 1_I
3
Parsimony

• ACCEFAHIK LKNPR
• ACCEFGHIL LLNPR
• ACDEFGHIK LINPK
• AADEFGHIL LNNPK
• I II III

1 K
3 K
L
L
2 L
4 L
Candidate tree 1_II
4
Parsimony

• ACCEFAHIK LKNPR
• ACCEFGHIL LLNPR
• ACDEFGHIK LINPK
• AADEFGHIL LNNPK
• I II III

Total number of substitutions for tree 1 4
1 R
3 K
K
R
2 R
4 K
Candidate tree 1_III
5
Parsimony

• ACCEFAHIK LKNPR
• ACCEFGHIL LLNPR
• ACDEFGHIK LINPK
• AADEFGHIL LNNPK
• I II III

1 C
2 C
D
D
3 D
4 D
Candidate tree 2_I
6
Parsimony

• ACCEFAHIK LKNPR
• ACCEFGHIL LLNPR
• ACDEFGHIK LINPK
• AADEFGHIL LNNPK
• I II III

1 K
2 L
L
K
3 K
4 L
Candidate tree 2_II
7
Parsimony

• ACCEFAHIK LKNPR
• ACCEFGHIL LLNPR
• ACDEFGHIK LINPK
• AADEFGHIL LNNPK
• I II III

Total number of substitutions for tree 2 5
1 R
2 R
K
K
3 K
4 K
Candidate tree 2_III
8
Parsimony

• ACCEFAHIK LKNPR
• ACCEFGHIL LLNPR
• ACDEFGHIK LINPK
• AADEFGHIL LNNPK
• I II III

1 C
2 C
D
D
4 D
3 D
Candidate tree 3_I
9
Parsimony

• ACCEFAHIK LKNPR
• ACCEFGHIL LLNPR
• ACDEFGHIK LINPK
• AADEFGHIL LNNPK
• I II III

1 K
2 L
K
K
4 L
3 K
Candidate tree 3_II
10
Parsimony

• ACCEFAHIK LKNPR
• ACCEFGHIL LLNPR
• ACDEFGHIK LINPK
• AADEFGHIL LNNPK
• I II III

Total number of substitutions for tree 3 6
1 R
2 R
K
K
4 K
3 K
Candidate tree 3_III
11
Parsimony

• ACCEFAHIK LKNPR
• ACCEFGHIL LLNPR
• ACDEFGHIK LINPK
• AADEFGHIL LNNPK
• I II III

Out of possible trees (1,2) (3,4) (4
substitutions) (1,3) (2,4) (5 substitutions)
and (1,4) (2,3) (6 substitutions) Tree (1,2)
(3,4) has the lowest number of substitutions.
This is the most parsimonious and therefore
most probable tree for this set of 4 sequences
1
3
2
4
Optimal tree