E8: Phylogenetic Tree

What is a phylogenetic tree?

A phylogenetic tree is a branching diagram that shows the evolutionary relationships among organisms based on similarities and differences in their DNA sequences.

What does a phylogenetic tree represent?

1. Evolutionary history 2. Common ancestry 3. Genetic relatedness

What is phylogenetics?

Phylogenetics is the study of evolutionary relationships using molecular, genetic, or morphological data.

Why are DNA sequences mainly used in molecular biology phylogenetics?

DNA reflects inherited genetic information.

What are the purposes of phylogenetic trees?

1. Determine evolutionary relationships 2. Identify related organisms 3. Compare species genetically 4. Trace ancestry 5. Study evolution 6. Identify unknown organisms 7. Analyze bacterial diversity

Why is DNA used in phylogenetics?

1. Closely related organisms have more similar DNA sequences 2. More similar DNA = closer evolutionary relationship 3. More sequence differences = more distant relationship

Why do sequence differences occur among organisms?

Mutations accumulate over time.

What are the important molecular biology topics connected to phylogenetics?

1. DNA Extraction 2. PCR Amplification 3. Primer Design 4. Gel Electrophoresis 5. DNA Sequencing 6. Cloning

What is the purpose of DNA extraction?

Obtain genomic DNA from organisms.

What is the purpose of PCR amplification in phylogenetics?

1. PCR amplifies target genes before sequencing 2. Sequencing requires large amounts of DNA

What are common genes amplified in PCR?

1. 16S rRNA gene in bacteria 2. COI gene in animals

What are characteristics of good primers?

1. Specific 2. Proper ™ 3. No dimers or hairpins

What is gel electrophoresis used for after PCR?

1. Confirm successful amplification 2. Verify fragment size

What is the purpose of DNA sequencing?

1. Determines exact nucleotide sequence of amplified DNA 2. Sequencing data becomes the basis for alignment, comparison, and phylogenetic tree construction

Why are PCR products sometimes cloned before sequencing?

1. Obtain pure DNA copies 2. Separate mixed DNA samples 3. Improve sequencing quality

What is the workflow of molecular phylogenetics?

1. Sample collection 2. DNA extraction 3. PCR amplification 4. Gel electrophoresis 5. DNA sequencing 6. Sequence alignment 7. Phylogenetic tree construction 8. Interpretation

What is an OTU?

OTU = Operational Taxonomic Unit.

What can an OTU represent?

1. Species 2. Strains 3. Sequence groups

What does each OTU become in the phylogenetic tree?

Each OTU becomes one branch in the tree.

What does the NCBI Nucleotide Database contain?

1. DNA sequences 2. Gene sequences 3. Reference organisms

What is FASTA format?

Sequences are stored in FASTA format.

What is sequence alignment?

Alignment arranges sequences to compare homologous positions.

What is the purpose of sequence alignment?

1. Identify similarities 2. Identify mutations 3. Compare organisms

What are common alignment tools?

1. ClustalW 2. MUSCLE

What are conserved regions useful for?

1. Primer design 2. Evolutionary comparison

What are variable regions useful for?

Differentiating species.

What do gaps represent?

Insertions & Deletions.

What are ambiguous bases?

Low-quality or unclear sequence regions.

What happens to ambiguous bases before tree construction?

Usually removed before tree construction.

What is MEGA software used for?

1. Sequence alignment 2. Evolutionary analysis 3. Phylogenetic tree construction

What are the components of a phylogenetic tree?

1. Branches 2. Nodes 3. Root 4. Tips/Leaves 5. Clade 6. Sister Taxa

What do branches represent?

Branches represent evolutionary lineages.

What do nodes represent?

1. Points where branches split 2. Common ancestors

What is the root of a phylogenetic tree?

The oldest common ancestor.

What do tips/leaves represent?

Organisms or OTUs.

What is a clade?

Ancestor and all descendants.

What are sister taxa?

Groups sharing immediate common ancestor.

What are the types of phylogenetic trees?

1. Rooted Tree 2. Unrooted Tree

What does a rooted tree show?

Evolutionary direction.

What does an unrooted tree show?

Relationships only.

What is evolutionary distance?

Evolutionary Distance is the amount of genetic difference between organisms.

What do more and fewer mutations indicate?

1. More mutations: Greater distance 2. Fewer mutations: Closer relationship

What is a mutation?

Mutation = change in DNA sequence.

What are the types of mutations?

1. Substitution 2. Insertion 3. Deletion

How are mutations used in phylogenetics?

Mutations accumulate over time and are used to infer evolutionary relationships.

What are the important terms in phylogenetics?

1. Phylogenetics – study of evolutionary relationships

2. Phylogenetic tree – relationship diagram

3. OTU – operational taxonomic unit

4. Node – common ancestor

5. Branch – evolutionary lineage

6. Clade – ancestor and descendants

7. Alignment – sequence comparison

8. Conserved region – similar DNA region

9. Variable region – mutation-rich region

10. Bootstrap value – branch reliability

11. Mutation – DNA sequence change

12. FASTA – sequence file format

What are the steps used to create a phylogenetic tree using molecular biology techniques?

1. Collect and isolate organisms 2. Perform DNA extraction 3. Use PCR amplification to amplify a target gene 4. Analyze PCR products through gel electrophoresis 5. Perform DNA sequencing 6. Save sequences in FASTA format and align them using software such as MEGA with tools like ClustalW or MUSCLE 7. Use phylogenetic analysis methods to construct the phylogenetic tree

Why is DNA extraction performed?

To obtain purified genomic DNA that will serve as the template for analysis.

Why is PCR amplification used in phylogenetic studies?

1. PCR amplifies a target gene commonly used in phylogenetic studies

2. PCR produces millions of copies of the gene for easier detection and sequencing

What components are required for PCR?

1. Template DNA 2. Primers 3. Taq DNA polymerase 4. dNTPs 5. Buffer

Why are primers designed to bind conserved regions?

So the same gene can be amplified among different organisms for comparison.

Why are PCR products analyzed through gel electrophoresis?

1. To confirm successful amplification 2. To check for DNA bands of the expected size 3. Incorrect or absent bands may indicate failed PCR

How is DNA sequencing commonly performed in this procedure?

Through Sanger sequencing, where ddNTPs terminate DNA elongation at different positions to determine the exact nucleotide sequence.

How are obtained sequences analyzed?

1. Sequences are saved in FASTA format 2. Sequences are aligned using software such as MEGA with tools like ClustalW or MUSCLE 3. Alignment is used to compare homologous nucleotide positions, identify mutations, and determine sequence similarities

What phylogenetic analysis methods are used to construct the phylogenetic tree?

1. Neighbor-Joining 2. Maximum Parsimony 3. Maximum Likelihood

Why do organisms cluster closer together on a phylogenetic tree?

Organisms with more similar DNA sequences are considered more closely related evolutionarily.