Population Genetics and Natural Selection

1. Population Genetics and Natural Selection Chapter 8 Microsatellite alleles for three loci depict genetic variation within a Great Tit population.

2. Definitions • Evolution – a change in gene frequencies in a population; may lead to speciation. • Natural Selection – differential reproduction and survival of individuals in a pop. due the environmental influences on the pop.; the environment affects fitness. • Offspring like parents • Variation among individuals is heritable. • More offspring than environment can support • Some individuals have higher fitness under particular environmental conditions.

3. Gene – a discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA • Alleles – alternative forms of a gene • Genotype – the genetic makeup of an individual • Phenotype – the physical and physiological traits of an organism Campbell and Reese 2002

4. Variation Within Populations • Phenotype is environmental and genetic • Variation in Plant Populations • Many plant species differ dramatically in form from one elevation to another (e.g. ) Potentilla glandulosa. • Distinctive ecotypes • locally adapted and genetically distinctive populations within a species. • Cross breeds produce viable seeds that are reproductive – not separate species.

5. Hypothesis: Morphology differences partly due to genetics. Null Hypothesis: No genetic difference; all environmental.

6. Hardy Weinberg • Hardy Weinberg principle states that in a population mating at random in the absence of evolutionary forces (natural selection), allele frequencies will remain constant. • The H-W Model allows for predicting genetic change due to environmental forces. • Hypothesis: environmental factor influences change in allele frequency change. • Null Hypothesis: allele frequency remains unchanged. 1 = (p+q)2 = p2+2pq+q2

7. Conditions Necessary for Hardy Weinberg • Random Mating • No Mutations • Large Population Size • No Immigration • Equitable Fitness Between All Genotypes • Likely, at least one of these will not be met and allele frequencies will change. • Potential for evolutionary change in natural populations is very great.

8. Natural Selection • Some individuals in a population, because of their phenotypic characteristics, produce more offspring that themselves live to reproduce. • Natural selection can favor, disfavor, or conserve the genetic make-up of a population.

9. Stabilizing Selection • Stabilizing selection acts to impede changes in a population by acting against extreme phenotypes and favoring average phenotypes.

10. Directional Selection • Directional selection leads to changes in phenotypes by favoring an extreme phenotype over other phenotypes in the population.

11. Disruptive Selection • Disruptive selection creates bimodal distributions by favoring two or more extreme phenotypes over the average phenotype in a population.

12. Change Due To Chance • Random processes can change gene frequencies in populations, especially in small populations. Called genetic drift. • Major concern of habitat fragmentation is reducing habitat availability to the point where genetic drift will reduce genetic diversity within natural populations.

13. Genetic Variation In Island Populations • In general, genetic variation is lower in isolated and generally smaller, island populations. • Reduced genetic variation indicates a lower potential for a population to evolve.

14. Microsatellite Analysis

15. Whose your Daddy?

16. Linkage to social function(Young and Hammock, 2005) http://www.nsf.gov/news/news_images.jsp?cntn_id=104238&org=NSF