BSC 219

Evolutionary Biology

12/4/12

26.1 Organisms Evolve Through Genetic Change Occurring Within Populations.

“Nothing in Biology makes sense except in the light of Evolution”

Theodosius Dobzhansky

Evolution

Genetic change taking place in a group of organisms over time.

Evolution includes genetic change only.

Evolution takes place in groups of organisms; what evolves is the gene pool common to a group of organisms.

Evolution

Anagenesis

Evolution taking place in a single group (a lineage) with the passage of time.

Cladogenesis

The splitting of one lineage into two, new species arise through cladogenesis.

Protein variation

Measures of genetic variation-changes in DNA and how they are reflected in amino acid sequence and protein function

Protein variation

Neutral-mutation hypothesis

Individuals with different molecular variants have equal fitness at realistic population size.

Balance hypothesis

Genetic variation in natural populations is maintained by selection that favors variation

DNA sequence variation

Restriction-site variation

Microsatellite variation

Variation detected by DNA sequencing

The Biological Species Concept (Ernst Mayer, 1942)

A group of organisms whose members are capable of interbreeding with one another but are reproductively isolated from the members of other species.

Prezygotic reproductive isolating mechanism

Ecological

Behavioral

Temporal

Mechanical

gametical

Allopatric speciation

When a geographic barrier splits a population into two or more groups and prevents gene flow between the isolated groups.

Sympatric speciation

Arises in the absence of any geographic barrier to gene flow; reproductive isolation mechanisms evolve within a single interbreeding population.

Speciation through polyploidy

Genetic differentiation Associated With Speciation

How much genetic differentiation is required for reproductive isolation to take place?

No universal answer! Can be up to 200 genes or down to less than 10 genes.

Phylogeny

The evolutionary relationships among a group of organisms are termed a phylogeny.

The Construction of Phylogenetic Trees

Distance approach

Parsimony approach

Infers phylogenetic relationships on the basis of the minimum number of evolutionary changes that must have taken place since the organisms last had an ancestor in common.

26.5 Patterns of Evolution Are Revealed By Changes at the Molecular Level

Rates of Evolution

26.5 Patterns of Evolution Are Revealed By Changes at the Molecular Level

The Molecular Clock

Measure the rate at which a protein evolves is roughly constant over time, the amount of molecular change that a protein has undergone can be used as a clock.

26.5 Patterns of Evolution Are Revealed By Changes at the Molecular Level

Genome Evolution

Exon shuffling

Gene duplication

Multigene family concept

26.5 Patterns of Evolution Are Revealed By Changes at the Molecular Level

Genome Evolution

Whole-genome duplication

Horizontal gene transfer