Download Population Genetics, Speciation, and Classification

Population Genetics, Speciation,
and Classification
Population Genetics
• Definition: study of evolution from a genetic
point of view.
• Microevolution: Change in the collective
genetic material of a population.
• Within a population, individuals may vary in
observable traits. Scientists use a bell curve to
show the frequency of traits.
Causes of variation
• Mutations: random, passed to offspring
• Recombination: Reshuffling of genes
• Random pairing of gametes: Because each
organism produces large numbers of gametes,
the union of particular gametes is by chance.
Gene Pool
• Total genetic
information available in
a population.
Allele Frequency
• If you knew all of the
alleles that are present,
then you could predict
expected genotypes
and frequencies of
alleles.
Hardy-Weinberg Genetic Equilibrium
• The Hardy-Weinberg Theorem states that the allele
frequencies of a gene in a population will remain constant,
as long as evolutionary forces are not acting. H-W therefore
provides a baseline, for a population that is not evolving.
For a population to be in H-W equilibrium, the following
conditions or assumptions must be met:
• 1. The population is very large; there is no genetic drift
2. Matings are random
3. There is no mutation
4. There is no migration
5. There is no selection
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If one of these conditions is broken, an evolutionary force is acting to change allele
frequencies, and the population may not be in H-W equilibrium. Natural
populations probably seldom meet all of these conditions; H-W provides a nice
model to study evolution via deviations from H-W equilibrium.
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Hardy Weinberg Equation
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Basic Relations
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A = dominant allele
a = recessive allele
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p+q=1
Where p = frequency of A allele
q = frequency of a allele
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p2 + 2pq + q2 = 1
Where p2 = frequency of AA genotype
2pq = frequency of Aa genotype
q2 = frequency of aa genotype
Gene flow
• Process of genes moving from one population
to another. Can happen through immigration
or emigration.
Genetic Drift
• Phenomenon by which
allele frequencies in a
ppulation change as a
result of random
events, or chance.
• Ex endangered
species, cheetas
Types of Natural selection
• Stabilizing- Those with the average form of a
trait have the highest fitness.
• Disruptive- Those with either extreme
variation of a trait have greater fitness.
• Directional- Those that display one extreme
form of a trait have greater fitness than
individuals with an average form of the trait.
Morphological species concept
• Morphological concept: Based on external and
internal structures. Same species?
Biological Species concept
• Proposed by Ernst Mayr, a species is a
population of organisms that can successfully
interbred but cannot breed with other groups.
• West vs. East medowlark do not recognize
each other’s song; so they do not interbreed.
Geographic isolation
• Physical separation of members of a
population.
• Allopatric speciation- happens when species
arise as a result of geogrphic isolation
• Allopatric=“different homelands”
Reproductive isolation
• Results from barriers to successful breeding
between population in the same area.
• Sympatric speciation
-When 2 subpopulations
Arise due to reproductive
Isolation.
Biodiversity
• Varieties of organisms considered at all levels,
from populations to ecosystems.
Taxonomy
• Science of describing, naming, and classifying
organisms.
• Any particular group within a taxonomic
system is called a taxon.
• Aristotle classified organisms based on where
they lived: land, water, air.
• Problems? How would a frog be classified?
Linnaean system
• Categorized based on form and structure.
Binomial Nomenclature
• Species or Scientific name with 2 parts
• Genus species
Homo sapiens
• Latin roots
• Subspecies: Variations of a species that live in
different geographic locations.
Phylogenetics
• Phylogeny-evolutionary history of a species or
a taxon.
• Phylogenetics- the analysis of the evolutionary
or ancestral relationships among taxa.
Evidence
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Fossils
Homologous features
Embryological features
DNA
Amino acid sequence
Chromosomes
Modern classification
• Domains- bacteria, Archaea, Eukarya
Brain pop video
• http://glencoe.mcgrawhill.com/sites/dl/free/0078802849/164213/00
044691.html