Evolution is a change in the allele frequency of a population.

TERMS TO REVIEW: gene, chromosome, homologous chromosomes, allele, locus (loci), dominant, recessive, homozygous, heterozygous, haploid, diploid, phenotype, genotype, gene pool

The mechanisms of heredity
	genes unknown in Darwin's time
	Mendel's theory rediscovered 1900
	at first scientists used Mendel's work to discredit Darwinian evolution
	later (1920's) determined that laws of inheritance explain genetic variation

Population Genetics

Study of the properties of genes within populations

Puts together Darwinism and Mendelian inheritance

Evolution results from changes in allele frequency

Population

Species

Gene pool

Modern synthesis--forged the contributions of genetics, Darwinism and paleontology.
	1.  Populations contain genetic variation that arises by random 
		    mutation and recombination.
	2.  Populations evolve by changes in gene frequency brought about by random 
		    genetic drift, gene flow and especially natural selection.
	3.  Most adaptive changes are gradual.
	4.  Diversification comes about by speciation, which ordinarily entails the gradual 
		    evolution of reproductive isolation among populations.
	5.  These processes, continued for sufficiently long periods, give rise to changes of 
		    such great magnitude as to warrant the designation of higher taxonomic levels.

The Hardy-Weinberg Theorem

States that there will be no change in allele frequencies in a population if the following 5 conditions are maintained: (See page 449 in your text also)

Very large population

No migration

No net mutations

Random mating

No natural selection

In a population meeting all these conditions, no evolution is occurring. It is in Hardy-Weinberg equilibrium.

All these conditions are never met.

The Hardy-Weinberg Equation - Fig 23.3a and Fig 23.3b.

Frequency of dominant allele = p

Frequency of recessive allele = q

              p + q = 1

To represent the individual which has received one allele from each parent:

            (p + q)2 = p2 + 2pq + q2 = 1    (the small 2 represents "squared")

Microevolution: Why Do Allele Frequencies Change?

Genetic Drift - change in frequency or even loss of alleles in small populations compared to large ones. Fig 23.4.

    

    Bottle neck effect - Fig 23.5

       cheetahs

    Founder principle

 

Natural Selection

 

Gene flow - Migration - Fig 23.6

 

Mutation

Genetic variation within populations

Quantitative characters

 

Discrete characters

 

Polymorphism

 

Measuring genetic diversity

   gene diversity

   nucleotide diversity

Variations between populations

Geographic variation - Fig 23.9

Cline - Fig 23.8

Sources of genetic variation

Mutations

Crossing over in meiosis

Independent assortment

Sexual recombination

Diploidy and balanced polymorphism preserve variation

heterozygote advantage sickle-cell anemia and malaria- Fig 23.10

frequency-dependent selection Fig 23.11

neutral variation

Selection In Action

Individuals best suited to environment are most likely to survive, mate and leave the most progeny

Individuals are selected, but populations evolve.

Individual alleles make varying contributions to fitness

Only natural selection produces adaptive evolutionary change

Darwinian fitness

relative fitness

Forms of Selection - summary of 3 forms from Solomon or Fig 23.12

Stabilizing selection

Diversifying selection - Fig 23.14

Directional selection

Natural selection maintains sexual reproduction - Fig 23.15

Sexual selection Fig 23.16

sexual dimorphism male peacock

intrasexual selection

intersexual selection

Natural selection cannot make perfect organisms

limited by historical constraints

compromises

not all adaptive

can only edit existing variations