The Genetical Theory of Natural Selection Chapter 6 Slide 2
1.Fitness definition 2.Modes and models of selection General model
of selection Directional selection Ex: Warfarin Stabilizing
selection Ex: Sickle cell anemia and birth weight Diversifying
selection Ex: Seedcracker finch Frequency dependent selection
3.Natural selection outcomes 4.Strength of selection Lecture
Outline Slide 3 Points to keep in mind about natural selection:
1.Natural selection is not the same as evolution Origin of Genetic
Variation Mutation + RecombinationGenetic Drift + Natural Selection
Changes in the Frequency of Alleles and Genotypes 2.Natural
selection can have no evolutionary effect unless phenotypes differ
in genotypes 3.A feature cannot evolve by natural selection unless
it makes a positive contribution to the reproduction or survival of
individuals that bear it Natural selection proceeds independently
at different loci Evolution Slide 4 Fitness Defining Fitness Arnold
Alois Schwarzenegger Homo sapiens Slide 5 Fitness Defining Fitness
The fitness of a genotype is the average lifetime contribution of
individuals of that genotype to the population after one or more
generations, measured at the same stage in the life history
Absolute Fitness ( R i )Per capita growth rate of each genotype i
Relative Fitness ( W i )Is the absolute fitness of genotype i
relative to the absolute fitness of a reference genotype ( R * )
Slide 6 Fitness Components of Fitness Individual Viability
Probability of survival of the genotype to reproductive age Mating
Success Number of mates obtained by an individual (Sexual
Selection) Z YGOTIC S ELECTION Fecundity Number of viable offspring
per female G AMETE S ELECTION Segregation Distortion Probability of
being segregated to the gamete Gamete Viability Probability of
survival of the gamete to fertilization Fertilization Success
Gametes ability to fertilize an ovum Slide 7 Models of Selection
Assumptions: large population, random mating, no mutation or
migration, viability selection only, discrete generations 1 Locus 2
Alleles A 1 p A 2 1-p=q next generation p we are interested in the
change of frequency from one generation to the next p-p=p if p>0
frequency of A 1 increase p
