Evolution of Populations 2010. The Modern Synthesis Population genetics integrates Darwinian evolution and Mendelian Genetics Important terms in population.

Evolution of Populations

2010

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

Gene Flow• Genetic exchange through migration – gain or

loss of alleles

MutationSubstitutes one allele for another

Selection Types

Sexual Selection

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

Major Lineages of Life

3 domains: Bacteria,

Eukaryota, Arachae