This document provides instructions for constructing a phylogenetic tree using maximum likelihood methods in PhyML. It describes collecting homologous sequences, aligning them with tools like ClustalW, manually editing the alignment, selecting an appropriate substitution model with programs like jModelTest, running PhyML with the alignment and model to generate an initial tree, and then iteratively improving the tree by removing rogue taxa and refining the process until a satisfactory tree is produced.
It includes the information related to a bioinformatics tool BLAST (Basic Local Alignment Search Tool), BLAST is in-silico hybridisation to find regions of similarity between biological sequences. The program compares nucleotide or protein sequences to sequence databases and calculates the statistical significance. This presentation too contains the input - output format, Blast process and its types .
It includes the information related to a bioinformatics tool BLAST (Basic Local Alignment Search Tool), BLAST is in-silico hybridisation to find regions of similarity between biological sequences. The program compares nucleotide or protein sequences to sequence databases and calculates the statistical significance. This presentation too contains the input - output format, Blast process and its types .
lecture for doctorate students while I was working as researcher assisstance about phylogenetic science, definition,
Understand the most basic concepts of phylogeny
Understand the difference between orthology, paralogy and xenology.
Be able to compute simple phylogenetic trees
Understand what bootstrapping means in phylogeny
Performance Improvement of BLAST with Use of MSA Techniques to Search Ancesto...journal ijrtem
process in which instead comparing whole query sequence with database sequence it breaks
query sequence into small words and these words are used to align patterns. it uses heuristic method which
make it faster than earlier smith-waterman algorithm. But due small query sequence used for align in case of
very large database with complex queries it may perform poor. To remove this draw back we suggest by using
MSA tools which can filter database in by removing unnecessary sequences from data. This sorted data set then
applies to BLAST which can then indentify relationship among them i.e. HOMOLOGS, ORTHOLOGS,
PARALOGS. The proposed system can be further use to find relation among two persons or used to create
family tree. Ortholog is interesting for a wide range of bioinformatics analyses, including functional annotation,
phylogenetic inference, or genome evolution. This system describes and motivates the algorithm for predicting
orthologous relationships among complete genomes. The algorithm takes a pairwise approach, thus neither
requiring tree reconstruction nor reconciliation
Performance Improvement of BLAST with Use of MSA Techniques to Search Ancesto...IJRTEMJOURNAL
BLAST is most popular sequence alignment tool used to align bioinformatics patterns. It uses
local alignment process in which instead comparing whole query sequence with database sequence it breaks
query sequence into small words and these words are used to align patterns. it uses heuristic method which
make it faster than earlier smith-waterman algorithm. But due small query sequence used for align in case of
very large database with complex queries it may perform poor. To remove this draw back we suggest by using
MSA tools which can filter database in by removing unnecessary sequences from data. This sorted data set then
applies to BLAST which can then indentify relationship among them i.e. HOMOLOGS, ORTHOLOGS,
PARALOGS. The proposed system can be further use to find relation among two persons or used to create
family tree. Ortholog is interesting for a wide range of bioinformatics analyses, including functional annotation,
phylogenetic inference, or genome evolution. This system describes and motivates the algorithm for predicting
orthologous relationships among complete genomes. The algorithm takes a pairwise approach, thus neither
requiring tree reconstruction nor reconciliation
lecture for doctorate students while I was working as researcher assisstance about phylogenetic science, definition,
Understand the most basic concepts of phylogeny
Understand the difference between orthology, paralogy and xenology.
Be able to compute simple phylogenetic trees
Understand what bootstrapping means in phylogeny
Performance Improvement of BLAST with Use of MSA Techniques to Search Ancesto...journal ijrtem
process in which instead comparing whole query sequence with database sequence it breaks
query sequence into small words and these words are used to align patterns. it uses heuristic method which
make it faster than earlier smith-waterman algorithm. But due small query sequence used for align in case of
very large database with complex queries it may perform poor. To remove this draw back we suggest by using
MSA tools which can filter database in by removing unnecessary sequences from data. This sorted data set then
applies to BLAST which can then indentify relationship among them i.e. HOMOLOGS, ORTHOLOGS,
PARALOGS. The proposed system can be further use to find relation among two persons or used to create
family tree. Ortholog is interesting for a wide range of bioinformatics analyses, including functional annotation,
phylogenetic inference, or genome evolution. This system describes and motivates the algorithm for predicting
orthologous relationships among complete genomes. The algorithm takes a pairwise approach, thus neither
requiring tree reconstruction nor reconciliation
Performance Improvement of BLAST with Use of MSA Techniques to Search Ancesto...IJRTEMJOURNAL
BLAST is most popular sequence alignment tool used to align bioinformatics patterns. It uses
local alignment process in which instead comparing whole query sequence with database sequence it breaks
query sequence into small words and these words are used to align patterns. it uses heuristic method which
make it faster than earlier smith-waterman algorithm. But due small query sequence used for align in case of
very large database with complex queries it may perform poor. To remove this draw back we suggest by using
MSA tools which can filter database in by removing unnecessary sequences from data. This sorted data set then
applies to BLAST which can then indentify relationship among them i.e. HOMOLOGS, ORTHOLOGS,
PARALOGS. The proposed system can be further use to find relation among two persons or used to create
family tree. Ortholog is interesting for a wide range of bioinformatics analyses, including functional annotation,
phylogenetic inference, or genome evolution. This system describes and motivates the algorithm for predicting
orthologous relationships among complete genomes. The algorithm takes a pairwise approach, thus neither
requiring tree reconstruction nor reconciliation
Course slides for computational phyloinformatics, an annual course organized by NESCent in collaboration with hosting organizations across the world. I am the teacher of the Perl section of the course, these are the slides I presented in 2010 at BGI, Shenzhen, PRC.
International Journal of Computer Science, Engineering and Information Techno...IJCSEIT Journal
In the field of proteomics because of more data is added, the computational methods need to be more
efficient. The part of molecular sequences is functionally more important to the molecule which is more
resistant to change. To ensure the reliability of sequence alignment, comparative approaches are used. The
problem of multiple sequence alignment is a proposition of evolutionary history. For each column in the
alignment, the explicit homologous correspondence of each individual sequence position is established. The
different pair-wise sequence alignment methods are elaborated in the present work. But these methods are
only used for aligning the limited number of sequences having small sequence length. For aligning
sequences based on the local alignment with consensus sequences, a new method is introduced. From NCBI
databank triticum wheat varieties are loaded. Phylogenetic trees are constructed for divided parts of
dataset. A single new tree is constructed from previous generated trees using advanced pruning technique.
Then, the closely related sequences are extracted by applying threshold conditions and by using shift
operations in the both directions optimal sequence alignment is obtained.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
1. Re-construction of Phylogenetic tree
using maximum-likelihood methods
PhyML (in nutshell)
Note: Slides are still under revision
2. Steps
• Collect homologous sequences.
• Multiple sequence alignment.
• Manually Curing of the multiple sequence alignment.
• Feeding the MSA to programs to study the substitution
rates in between locations of the sites in the MSA.
(ProtTest for protein and jModeltest for DNA alignments).
• Selecting an appropriate substitution model.
• Feeding the MSA, starting tree (e.g., those obtained with
Neighbour-joining method) and substitution model as well
as bootstrap properties to PhyML.
• Obtain tree and cross-check bootstrap values, branch
length and general resolution.
• Remove rouge taxons and redo the entire process till
satisfactory tree is constructed.
3. Selection of sequences for phylogenetic tree
Purpose of the tree
1.Geneology: evolution of gene/ gene family irrespective of
speciation (called gene tree).
2.Phenology: evolution of gene/gene family in context of
phylogenetic speciation (called species tree).
Homologues: Genes derived from common ancestors.
Orthologues: Genes derived from common ancestors or
homologues that are separated from each other by
gene/genome duplication (of course before speciation).
Paralogues: Genes derived from common ancestors or
homologues that are separated from one another by
speciation (i.e., after speciation occurs the same copy of gene
evolves under different constraints that are face by the two
different species.
4. Selecting sequences
•Similar sequence of considerably low e-value in BLAST in
general can be assigned to be homologous.
•<40% amino acid similarity = higher by-chance appearance of
similarity and not necessarily a similairity due to homology
•~40% amino acid similarity= twilight zone for homology (may
be may not be)
•≥60% amino acid similarity=homology inferred
(~80% or higher similarity in DNA sequence.)
5. • Perform BLAST of the new sequence.
• Note the hits obtained and the e-value.
• Follow the sequences down the list with increasing e-values till the e-
value suddenly jumps in order of 3 or so. E.g. 1e-10 means that the
possibility that the sequence similarity is having a by-chance occurance is
in probablity of 1x 10-10
and not due to homology. A sudden jump from 1e-
10 to 1 e-5 in the similarity sequence BLAST result list may indicate that
the homology may be limited till the sequences with lower e-value.
(Note: e-value is subjected to the size of the sequence database. larger
database have lower starting e-values for a given query sequence)
• Note the annotation or characterization of the proteins encoded as well
as the % similarity and sequence coverage.
• Also note the organisms from which it is derived
• Select sequences with considerable coverage and similarity for multiple
sequence alignment.
• The choice of sequence can be based on species of origin and their
relatedness or on special activities and multiple domain structures
depending on what basis the phylogeny is to be re-constructed.
6. MSA- Multiuple Sequence Alignment
Different types eg., CLUSTAL, DiALIGN, MUSCLE, MAFFT.
THEORETICALY ANY SEQUENCE CAN BE ALIGNED TO ANY OTHER SEQUENCE>
WHETHER IT MAKES SENSE OR NOT IS A DIFFERENT ISSUE.
CLUSTAL (CLUSTALW2, X): ClustalW2 uses a dynamic programing method to make
MSA based on Hidden-Markov models (HMM) of probalistic likelihoods of all gaps,
matches and mismatches to be aligned into a biologically relevant MSA. The dynamic
programing stepwise finds the highest score of MSA based on cumulative scores by
matches at each base and penalizing scores due to mismatches. This stepwise scoring
is decided in first a pairwise matrix choosing the shortest distance to higher scores in
situations where gaps are observed. (more info on internet will be available). This
reduces greatly the time required for analysis.
DiALIGN: Dialign which does not use gap penalizing and thus can be used for more
accurate alignment of very divergent sequences that suffer large alignment gaps.
MUSCLE: MUSCLE (Multiple Sequence Alignment by Log-Expectation) rely on
interative methods that involve repeatedly aligning the old sequences while adding
newer to the growing MSA to produce more accurate alignments in shorter time
frames.
7. CLUSTAL (CLUSTALX):
•Feed sequence in fasta format (copy paste on the applet or attach a
notepad file {*.txt}).
E.g., > (name of the 1st
sequence)
Agtgatagatag…………
>(name of the 2nd
sequence)
Gatagatcgctgatcgctc…..
•Run with default.
•Analyze
Gaps are frequent: change the settings such that gap
opening penalty is high e.g. increase from the default value
of 10 to 15, 20, 25, 30.
Gaps are long but less frequent: change settings such that
gap extension penalty is high e.g., increase from default
value of 1 to 2,3,4,5
No gaps but many mismatches: relax the gap opening (5,
6, 7,) and/or gap extension penalty (0.1, 0.2, 0.4, 0.5) such
that indels might occur in the data set for a better match.
REDO THE MSA ALIGNMENT TILL IT IS better.
8. Manual curing of MSA
•Involves intellectual curing of usually the placement of alignment gaps
among the sequence alignment. This is understood more appropriately in
case to case study.
•Involves the removal of rouge taxons. i.e., the sequence that do not fit in
the current MSA due to dis-proportionate accurence of mismatches and
gaps. Usually it can be figured out after the first tree is made and the
bootstrapping values and/or branch lengths of the particular lineages is
questionable. (appropriate software are available).
•Larger the sequence set the higher the accuracy of the tree. But also more
time consuming is tree construction by maximum likelihood (ML).
•More diverse the sequence set more erroneous the tree may be since it
would be an approximation. Hence closely similar sequences
representatives from each ordered data set needs to be selected. For eg.,
when talking of small molecule methyl transferases one may take a few
close relatives of O-, N-, C- methyl transferases for analysis since these
have considerable phylogenetic homology.
9. Substitution model
•The curated MSA can be included as an input to programs like jModeltest for DNA and
Prottest for proteins to the pattern of substitution at each site in the MSA. Based on this
pattern a list of appropriate substitution model for anaylsis is calculated. For eg. The
simplest model Jukes-Cantor (JC) says that each base of DNA can be substituted at equal
rate to other base in evolution. Though it is unrealistic in the practicality of life but the
sequences selected might just anticipated to be obliging to this rate and thus JC can be
used for analysis in PhyML. Kimura model says that transitions (Ts) (or purine to purine and
pyrimidine to pyrimidine changes) and transversions (Tv) (purine to pyrimidine or vice
versa) changes occur at different rates.
•There are 22 DNA substitution models published and each model can have slight variants
based on statistical distribution of variables like +I + G and +Y thus making it a total of
22*4=88 substitution model for DNA substitution.
•+I: refers to proportion of invariable sites. (invariable sites refers to the bias incorporated
due to substitution and rate heterogeneity amongst different lineages).
Inclusion of this parameter ensures that the bias of sequence dissimilarity due to sequence
relatedness id reduced.
•+g: refers to gamma distribution of the matrix (gamma distribution is a pattern/shaape
that is obserevd during statistical distribution of variants).
•+y: refers to distribution or accounting for Ts/Tv ratio (incorporated due to slight
variations observed between transition and transversion substitutions).
e.g., MSA can follow a JC model or JC+I or JC+G or JC+Y
10. Substitution model
•The decision of what substitution model depends on three sattistical
considerations incorporated in both jModeltest and prottest. Akaike
Information Criteria (AIC), Bayesian Information criteria (BIC) and Akaike
Information Criteria corrected for small samples (AICc).
•The model having high scores for AIC and BIC are usually selected as
appropriate substitution models for phylogenetic estimation.
Phylogeny
PhyML at present incorporates analysis using 32 substitution models for
DNA.
After adding all the tested parameters like MSA, substitution models, + I/
+G/+Y parameter options the tree building can be carried out.
PhyML requires a strating user-define tree for building a phlylogenetic tree.
If not available PhyML can be commanded to construct by its own a
Neighbour-Joining starting tree.
The tree can be improved by selecting option like SPR +NNI so that
appropriateness in branch lengths can be incorporated.
Finally a bootstrapping for 1000 pseudoreplicates is choosen for accuracy
of branch topology.
11. Bootstrapping
Bootstrapping involves the program to perform the same
tree building with pseudoreplicates of the sequences
after breaking blocks of alignment and rearranging and
then calculation how many times per hundred
pseudoreplicates does a branch fall under the same
topology.
A bootstrap of greated than 70% is significant in general.
Higher amount of pseudoreplicates chooses the more
accurate is the topological calculations
A bootstrap pesudoreplicate of 1000 is preferable but in
consideration of time required pseudoreplicate of 100
also suffices.
12. Re-construction
•Once the tree is generated, the tree is broadly looked upon for
accuracy by bootstrap values of each branch as well as disproportionate
branch lengths.
•In case of faulty trees, corrections need to be made at both aspects.
•If the MSA is cured properly, then one might need to remove rogue
taxons (Taxons that are problematic to the tree topology or branch
length) using available softwares.
The entire process from searching for optimal substitution models
may needed to be repeated.
•If no rogue taxons can be identified. Reducing the generality of
sequence diversity could also be tried. And more relevant sequences
only be included in MSA.
•The NJ tree option can also be changed to a user defined tree option.
•The tree construction is repeated in a number of cycles untill
appropriate tree is generated.