- A phylogenetic tree represents a hypothesis about evolutionary relationship.
- Each BRANCH POINT represents divergence of two species.
- SISTER TAXA are groups that share an immediate common ancestor.
- A POLYTOMY is a branch from which more than two groups emerge.
Tree requiring fewest evolutionary
events (Appearances of shared derived characters) is the most likely.
Given certain rules about how DNA changes over time
a tree can be found that reflects the most likely sequence
of evolutionary events
Linking classification and
phylogeny
- Systematists depict evolutionary relationships in branching phylogenetic trees.
- Linnaean classification and phylogeny can differ from each other.
- Systematics have proposed the phylocode which recognizes only groups that include a common ancestor and all its descendants.
Maximum Parsimony
&
It is an evolutionary novelty unique to a particular clade.
Character originated in an ancestor of the taxon
An outgroup is a species or group of species from an evolutionary lineage that is known to have di-verged before the lineage that includes the species we are studying (the ingroup).
Shared ancestral & shared derived characters
Maximum Likelihood
Inferring Phylogenies Using Derived Characters
Outgroup & ingroup:
Shared derived
character:
Shared ancestral
character:
THE EVOLUTIONARY HISTORY OF
BIOLOGICAL DIVERSITY
&
PHYLOGENY AND TREE OF LIFE
New information continues
to revise our understanding
of the tree of life
In recent decades,
we have gained insight into even the very deepest branches of
the tree of life through molecular systematics.
A Simple Tree of All Life
- Eukaryotes & archea are more closely related to each other than bacteria.
- Based largely on rRNA genes as they have evolved slowly
- Substantial interchanges of genes between organisms in different domains.
Horizontal gene transfer:
Movement of genes from one genome to another.
It complicates efforts to build a tree of life.
What we can and cannot learn from phylogenetic trees?
- They do show pattern of descent.
- They donot indicate when species evolved or how much genetic change occured in a linneage.
- It should not be assumed that a taxon evolved from a taxon next to it.
- Branch length can determine chronological time and branching points can be determined from the fossil records.
For Example
Convergent evolution......
It occurs when similar environmental pressures and natural selection produce similar (analogous) adaptations in organisms from different evolutionary lineages.
Evaluating molecular homologies
- Systematists use computer programs and mathematical tools when analyzing comparable DNA segments from different organisms.
- Bat and bird wings are homologous as fore limbs but analogous as functional wings.
- Homology can be distinguished from analogy by comparing fossil evidence and the degree of complexity.
- These two DNA sequences from organisms that are not closely related coincidentally share 25% of their bases.
- It is important to distinguish homology from analogy in molecular similarities.
- Mathematical tools help to identify molecular homoplasies or coincidences.
- Molecular systematics uses DNA and other molecular data to determine evolutionary relationships.
Hina Shafique
Samina bano
Group members:
From the Greek meaning“single tribe”signifying that it consists of an ancestral species and all its descendants
Cladistics
- Groups organisms by common descent.
- A clade is a group of species that includes an ancesstoral species and all its descendants.
- Clades can be nested in larger clades but not all grouping of organisms qualify as clades.
Meaning "beside the tribe" signifying a group which consists of an ancestral species and some, but not all of its descendants
Meaning “many tribes” signifying a group, which includes taxa with different ancesstors.
Neutral theory
"Much evolutionary change in genes and proteins has no effect on fitness & therefore is not influenced by darwinian selection"
Rate of molecular change in these genes
& proteins should be regular like a clock
"All evolved independently"
- Common features:
- An elongated body
- Enlarged front
- Paws
- Small eyes
- A pad of thickened skin that protects a tapered nose
Marsupial Australian “mole”
Analogy
When constructing a phylogeny systematists need to distinguish whether similarity is the result of homology or anology.
Homology
Investigating the Tree of Life
Phylogeny:
- the evolu-tionary history of a species or group of species.
SYSTEMATICS:
- this discipline classifies organisms and determine their evolutionary relationships.
- systematics use fossil ,molecular and genetic data to infer evolutionary relationships.
taxonomy:
An organism’s evolutionary
history is documented
in its genome
- it is the ordered division and naming of organisms.
- introduced by Carolus Linnaeus.
Molecular clocks help track
evolutionary time
Hierarchical classification
- Species epithet
- Unique for each species
Binomial nomenclature
- Genus name
- First letter capital
1-Two part name for species-Binomial nomenclature
2-Hierarchical classification
Two key features of this system:
Phylogenetic Trees with Proportional
Branch Lengths
- Comparing nucliec acids or other molecules
- DNA that codes for rRNA changes relatively slowly .
- It is useful for investigating branching points hundreds of million years ago.
- mtDNA evolves rapidly & can be used to explore recent evolutionary events.
In some trees length of a branch can reflect the number of genetic changes that have taken place in a particular DNA sequence in that lineage.
- Tree constructed by comparing sequences of a homologous gene that plays a role in development.
- The Drosophila gene was used as an outgroup.
- The branch lengths are proportional to the amount of genetic change in each lineage.
- The varying branch lengths indicate that the gene has evolved at slightly different rates in the different lineages.
- We must make an assumption about how change occurs over time.
- A molecular clock uses constant rates of evolution in some genes to estimate the absolute time of evolutionary change.
- They are calibrated against branches whose dates are known from the fossil record.
Difficulties with molecular clocks
From Two Kingdoms to Three Domains
- It does not run as smoothly as neutral theory predicts.
- Irregularities result from natural selection in which some DNA changes are favored over others.
- Estimates of evolutionary divergences older than the fossil records have a high degree of uncertainty.
- The use of multiple genes may improve estimates.
- Early taxonomists: only two groups plants & animals.
- Later 5 kingdom system:Monera, protista, plantae, fungi & animalia.
- More recently: 3domain system : Bacteria, Archea & Eukarya.
A molecular clock for mammals
- The number of accumulated mutations in seven proteins increased over time in a consistent manner for most mammal species.
- The three green data points represent primate species, whose proteins appear to have evolved more slowly than those of other mammals.
- The divergence time for each data point was based on fossil evidence.
Current view of biological diversity
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