lesson 11 Flashcards
Maximum Parimony
Best tree uses fewest number of transitions to account for gains/losses of traits i.e., best tree is the tree with the fewest tick marks.
Assumes homoplasies (convergent traits) are rare.
Trees based on DNA sequence data are more reliable
Monophyletic group X contains sister taxa A & B.
X is a sister taxon of species C.
Neutral Theory / Molecular Clock enables us to estimate time/rate of divergence
- Calibrated using fossil record: number of nucleotide di!erences compared to branch point (=known fossil)
- Assumes no selection on DNA sites (introns) and mutation rate is constant
- Age of branch points can be discerned
Population:
A group of individuals from the same species living in the same area
Gene flow
The movement of genes (alleles) among populations due to migration of individuals.
Malaria resistance allele and the Du!y antigen
- Malarial parasites P. vivax and P. knowlesi exploit Du!y antigen receptor on red blood cells.
- Almost 100% Africans who live in Malaria infested regions are Du!y negative (=natural selection!)
- Most Europeans Du!y positive
What is speciation?
Reduction/elimination of gene flow among populations due to evolution of reproductive barriers.
Adaptations and Environment
Speciation is the result of natural selection
Separation occur in…….
Sympatry
Allopatric speciation
- One population fragments into two populations (e.g., due to a vicariance event).
- Isolated populations diverge (through mutation and natural selection) in mating characteristics (genetic, physiological, morphological, behavioral).
- Incompatible mating characteristics prevent the production of viable/fertile o!spring between members of the two populations (reproductive barriers)
- According to the Biological Species Concept, a new species has formed!
