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The Modern Synthesis• Population genetics integrates Darwinian evolution and
Mendelian Genetics• Important terms in population genetics:
Population: group of individuals of same species
Species: groups of populations that are capable of interbreeding and producing fertile offspring in nature
Gene pool: total aggregate of genes in a population
Hardy – Weinberg Theorem• Gene pool of non-evolving population
• States that the frequency of alleles and genotypes in a population’s gene pool remain constant unless acted upon by agents other than Mendelian segregation and recombination of alleles. p+q = 1
Hardy Weinberg Equilibrium:
p2 + 2pq + q2 = 1 P2 = Frequency of RR phenotype2pq -= Frequency of Rr phenotypeq2= Frequency of rr phenotype
Conditions that must be met:
1. Very large population size.2. No migration3. No net mutations4. Random mating5. No natural selection
Do you that any natural populations are in Hardy-Weinberg equilibrium?
Microevolution
• Generation to generation change in the population’s frequency of alleles
• 2 main causes: genetic drift – change due to chance, small populations & natural selection
• Other causes -
Bottleneck Effect• Drastically reduced population sizes• Small population size may not be
representative of original gene pool• Reduction in genetic variablility
The Founder EffectOccurs when a few individuals colonize an isolated habitat from a larger population
Speciation – Biological Species Concept
• Prezygotic Barriers: habitat isolation, behavioral isolation, temporal isolation, mechanical isolation, gametic isolation
• Postzygotic Barriers: reduced hybrid viability, reduced hybrid fertility, hybrid breakdown
Types of Speciation
• Allopatric: geographic barriers, disruption of gene flow
• Sympatric: genetic causes – polyploid (plants), other genetic factors
Tempo of Evolution
• Darwin – gradual continual rate• Punctuated equilibrium model: spurts of rapid
change followed by periods of relatively little change (Ex. Species exists for 5 million years but most morphological changes in 50,000 yrs – just 1%).
Phylogenies• Many lines of evidence compiled• Biogeographical, fossil, morphological
similarities (homologous not analogous structures), genetic evidence
Categories of Evolution• Convergent evolution - acquisition of the same
biological trait in unrelated lineages. • Leads to analogous structures
Parallel evolution is the development of a similar trait in related, but distinct, species descending from the same ancestor, but
from different clades
Divergent evolution - accumulation of differences between groups which can lead to the formation of new species, usually a result of diffusion of the same species
adapting to different environments