phylogeny

Phylogeny

The evolutionary history of a species or group of related species

Phylogenetic trees

Show the amount of change over time calibrated by the fossil record or a molecular clock

Cladograms

Phylogenetic trees without time scale or evolutionary difference between groups

Taxonomy

Process of naming and classifying organisms

Father of taxonomy

Carlous Linnaeus

Classification system

1. Binomial nomenclature

2. Taxons

Binomial nomeclature

Genus species; ALWAYS ITALICS

Taxons

Places organisms into groups that have biological meaning

Hierarchy classification

1. Domain

2. Kingdom

3. Phylum

4. Class

5. Order

6. Family

7. Genus

8. Species

Horizontal branch of the tree

Represents the evolutionary lineage

Branch point of the tree

Common ancestor of all the animal groups

What is learnt from phylogenetic trees

• Shows patterns of descent, not phenotypic similarity

• Sequence of branching does not indicate absolute time

• Nodes on a tree represent the most recent common ancestor of any two groups or lineages

• Taxa that are beside each other did not evoleve from each other, rather they share a common ancestor

Homology

Phenotypic and genetic similarities due to shared ancestry; organisms that share very similar morphologies or similar DNA sequences are likely to be more closely related than organisms with vastly different structures or sequences

Analogous structure

A similar structure in organisms due to convergent evolution (similar selection pressure)

Ways to separate homologous vs analagous

• DNA sequences and protein structure

• Fossil evidence

Shared ancestral character

A character that is shared by members of a particular group but that originated in an ancestor that is not a member of that group

Shared derived character

An evolutionary novelty unique to a particular group

Ingroup

The groups of species being studied in the cladogram

Outgroup

A group of organisms not belonging to the group whose evolutionary relationships are being investigated

Molecular clock

An approach for measuring the relative time of evolutionary change based on the observation that some genes and other regions of genomes appear to evolve at a constant rate

Underlying assumption

The number of nucleotides substitutions in related genes is proportional to the time that has elapsed since the genes branched from their common ancestor

How to draw molecular clock

Graph the number of genetic differences against the dates of the evolutionary branch points that are known from the fossil record

Problems with drawing molecular clock

Some parts of the genome have evolved in irregular bursts; average rate of change, not completely accurate

Differences in clock speed

• Some mutations are neutral: the mutation doesn’t affect the survival or reproduction rate of the organism

• Many mutations are harmful and will be selected against quickly these genes do not change much over time → highly conserved genes.