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MUN deadline Jan. 18, 2008?

Biology 4250 Evolutionary Genetics

Winter 2008

Dr. David Innes

Dr. Dawn Marshall

Course Webpage:

http://www.mun.ca/biology/dinnes/B4250/Biol4250.html

Evolutionary Genetics

Goals:- to understand the impact that evolutionary processes have on the patterns of genetic variation within and among populations or species

- to understand the consequences of these patterns of genetic variation for various evolutionary processes

Course Information

Tentative Outline of topics:

1. Introduction/History of Interest in Genetic Variation

2. Types of Molecular Markers

3. Molecular Evolution

4. Individuality and Relatedness

5. Population Demography, Structure & Phylogeography

6. Phylogenetic Methods & Species Level Phylogenies

7. Speciation, Hybridization and Introgression

8. Sex and Evolution

9. Forensic Applications

10. Human Evolutionary Genetics

11. Conservation Genetics

Course Information

Lecture format:

Mon, Tues lectures, Fri Discussion

Reading for Friday Jan. 11

From “Evolution”

http://www.mun.ca/biology/dinnes/B4250/Reading1.PDF

Labs: Mon. 2 – 5 pm starting Jan. 14Computer labs require a LabNet account

Evaluation

Midterm (Mon. Feb. 25) 20%

Final 30%

Laboratory exercises 20%

Term paper 15%

Presentation 10%

Participation 5%

History of Genetic Variation

Darwin and evolution:

conversion of variation between individuals to variation between

populations and species in time and space.

Population genetics:

- origin and dynamics of genetic variation within populations

- changes or stability of genes within populations and the rate of

divergence in genes between partially or wholly isolated populations

History of Genetic Variation

Evolution: adaptation, speciation, extinction

Contribution of population genetics to evolution

G1 genetic description of population at time t =1

G1’ genetic description of population at time t =1+1

P1, P2, G2 phenotypic and genotypic states of population

during transition

T1 – T4 transformation processes Lewontin (1974) Figure 1

T1 T2 T3 T4

G1 ---------> P1---------->P2----------->G2--------->G1’

History of Genetic Variation

T1 processes that determine the distribution of phenotypes that develop from various

genotypes in various environments

T2 processes of mating, migration and natural selection that transform the phenotypic

array in a population within a generation

T3 rules that translate the distribution of phenotypes (P2) into the associated

distribution of genotypes

T4 genetic rules (Mendel) that predict the array of genotypes in the next generation as

a function of gametogenesis, mating and fertilization

History of Genetic Variation

Population Genetic Theory (early-mid 1900):

 

Mendelian Genetics - Genotypes (genes, alleles)

Biometrical Genetics - Phenotypes

1. Mendelian Genetics: change in allele frequencies

Genotypes Fitness

 

A1A1 w11

 

A1A2 w12

 

A2A2 w22

 

Freq. (A1) = p Freq. (A2) = q

1. Mendelian Genetics:

p = allele frequency in current generation

 

p’ = allele frequency in next generation

 

w = p2w11+ 2pqw12 + q2w22 (population mean fitness)

 

 

change in allele frequency:

 

p’ = p(pw11+qw12)

w

 

ie. change a function of allele frequency and fitness

2. Biometrical Genetics: (change in phenotypes)

R = h2S 

R = Response = distribution of phenotypes in the next generation

S = Selection differential = difference in total distribution of phenotypes and

distribution of phenotypes that survive and reproduce

h2 = Heritability (VG / VP) proportion of total phenotypic variation (VP) that is due

to genetic variation (VG)

2. Mendelian Genetics and Biometrical Genetics

Therefore two approaches to studying evolutionary dynamics:

Genotypic (Mendelian)

Phenotypic (Biometrical)

 

However,

- fitnesses (w) a function of the phenotype

- heritabilities a function of genetic and phenotypic variances.

 

thus,

an understanding evolutionary processes requires an understanding of the relationship between genetic and phenotypic variation.

2. Mendelian Genetics and Biometrical Genetics

describing an evolutionary process within a population requires some information on the statistical distribution of genotypic frequencies. Therefore, empirical population genetics has centered around the characterization of genetic variation in populations. (Lewontin 1974)

Molecular Variation

Molecular ecology and evolution developed as a field of research > 1953 (DNA structure, proteins, 1986 PCR)

 

Research preoccupied with functional role and adaptive significance of genetic variation (functional molecular variation: natural selection at the level of proteins and DNA)

 

However,

molecular variation can also be used as genetic markers to study behaviour, natural history and phylogenetic relationships (ie. Neutral markers)

The role of Natural Selection in Maintaining Genetic variation

History: Classical-Balanced debate (< 1966)

Evolution: temporal change in genetic composition of populations

Measuring genetic variation required to reveal the operation of natural selection, mutation, genetic drift etc.

The role of Natural Selection in Maintaining Genetic variation

Problem: difficult to measure genetic variation

Theoretical population genetics being developed

- limited opportunity to apply theory to natural populations

Empirical Population genetics:

- colour polymorphisms

- chromosome variation

Natural Populations

Genetic variation:

1. Classical - low

2. Balanced - high

Source of genetic variation (new genotypic combinations)

Natural Populations

What fraction of genes is heterozygous in an individual and polymorphic in a population?

Answer requires an unbiased assay for polymorphic and monomorphic gene loci

Protein Electrophoresis

1966 Lewontin and Hubby

20 – 50 loci

Variant and invariant loci

Fruit flies and Humans

~ 30 % of loci polymorphic

~ 10 % of loci heterozygous

Protein Electrophoresis

Protein Electrophoresis

Protein Genetic Variation

Allele frequency data easily fit into existing population genetic theory

Refined techniques showed high levels of DNA sequence variation

Empirical data rejects the classical school

Genetic Variation

Does natural selection explain the observed high levels of genetic variation?

Could be determined by processes other than selection ie. neutral

Neutralist-Selectionist debate

Neutralists - Selectionists

Alternative alleles no differential fitness effects

Most molecular polymorphisms maintained by mutation input and random allelic extinction

Neutralists - Selectionists

Neutral theory became the

“Null Hypothesis”

Neutral theory a simpler explanation than natural selection

Requires only mutation rate, gene flow, population size