The Evolution of Populations•Darwin and Mendel’s discoveries merged.

•Darwin’s theory of natural selection•Mendel’s inheritable information

•Population Genetics: genetic variation within a population

•Modern Synthesis: 1940’s; integrated discoveriesPopulation is the unit of evolutionNatural selection is means of mechanismGradualism: large changes evolve from small changes over long period of time.

Genotype Frequencies

Population: Localized group of individuals belonging to the same species.

Species: Individuals that have the potential to interbreedand produce fertile offspring in nature.

Gene Pool: Total aggregate of genes in a population at any on time. Consists of all alleles at all gene loci inall individuals of the populationDiploid, locus, fixed pop.,

•Individuals are selected but•Populations evolve.

Imaginary Population of Flowers

• R is Dominant (Red), r is recessive (white)

• 500 plants (20 are white, HR)

• 480 are red meaning R? (HD or Ht)•IF

•320 are RR and 160 are Rr……then

1. How many copies of the gene are there in the population?

2. How many genes are dominant? Recessive?

3. What are the percentage of each

•1000 genes

•800 dominant

•200 recessive

•80%....20%

Hardy-Weinberg TheoremFrequencies of alleles and genotypes in a population’s gene poolremains constant over the generations unless acted upon by other agents. The number of times an allele occurs within a population.

p= frequency of dominant alleleq= frequency of recessive allele

p+q=1

Hardy Weinberg Equationp2 + 2pq + q2 = 1

Frequencyof AA

genotype

Frequencyof Aa +aAgenotype

Frequencyof aa

genotype

•PKU: recessive allele disease1 in 10,000 births (q2=0.0001)

•What percentage of US population are carriers?

Solution• One PKU per 10,000 births….

• q2 = 0.0001 frequencies of HR

•Therefore….q = √0.0001 = 0.01 Frequency of Reccesive Allele•Frequency of Allele is p + q = 1 and if q = 0.01•then p = 0.99•Now using HW Equation solve for 2pq•2pq = 2 x 0.99 x 0.01 = 0.0198 or close to 2%

•2% of the Population are PKU Carriers.

You Solve1. Allele Frequency of B is 0.7, what would the

frequency of heterozygotes by if in HW equilibrium? Frequency of recessive allele?

1. 313 out of 1432 individuals have a recessive disorder. What percentage of this population are carriers?

2. If 511 individual out of 2315 show the characteristic of a DOMINANT disorder, what is the frequency of the recessive allele? How many individuals would be show the recessive trait?

0.42 0.30

50%

0.53 648 INDIV.

MicroevolutionChanges of the gene pool of a population at the smallest level.Frequencies of Allele in a population.

5 Conditions needed for HW Eq.1. Very Large Populations: 2. Isolation from other populations3. No Net Mutations4. Random Mating5. No Natural Selection

•A deviation from HW eq. in a gene pool signifies evolution•Natural Population are not EXPECTED to be in HW eq.

5 Agents of Microevolution1. Genetic Drift: changes in the gene pool of a small population

Genetic Drift can be caused by:

A. Bottleneck effect: Disaster eliminates large population. Surviving population is not represented of the original. Genetic variability is low

B. The Founder Effect: Genetic drift may occur when a smaller colony breaks away from original. (Darwin’s Finches)

Cause of Microevolution Cont.

2. Gene Flow: genetic exchange due to alleles migrating in or out of a population. Will tend to reduce differences b/w populations.

3. Mutations: Change in DNA of an organism. Mustoccur in gametes, rare occurrence of this occurring.

Cause of Microevolution Cont.

4. Nonrandom Mating: “Inbreeding”; relative frequency of genotypes deviate from H-W.W/ each generation Heterozygote # decreases.Assortive Mating: selecting partners with similar characteristics.

5. Natural Selection: differential success of reproduction. Most likely agent to causemicroevolution. Selects favorable genotypes

Inheritable Variations•Differences can occur between populations

•Quantitative Variations occur along a continuum.•Polymorphism: Two or more contrasting forms (morphs) of a characteristic. High frequency of alleles of

all forms.Ex: garter snakes, freckles, Blood type (ABO).

Variation Between Populations

•Geographical Variations: differences b/w pop (or w/i). due to environmental factors. Natural selection andgenetic drift can cause.

Cline: graded change in a trait along a geographicaxis.

Mutations generate Genetic Variations

•Mutation: •Point mutations mostly harmless, occurin somatic cells. Rarely will cause mutantallele allowing for better reproduction success.

•Chromosomal Mutation: disrupts developmentmay have benefits.

•Bacteria: reproduce every 20 minutes, mutationin one may produce millions in an hour.Antibiotic resistant bacteria

Natural Selection as a means of Evolution

•Darwinian Fitness: the measure that is critical to selection, is the relative contribution anindividual makes to the gene pool of the next generation.

•Relative Fitness: contribution of a genotype to thenext generation compared to another. Based asa % based on best reproductive member (1).

•Diversifying Selection: environmental factorsfavors extreme individuals at both ends.

•Directional Selection: changes that occur whenmoving to new area with different conditions.

•Stabilizing Selection: cuts extreme varients, reduce phenotypic variation, status quo

Modes of Selections

Natural Selection and Perfection•Natural Selection cannot produce perfection•WHY???

1. Evolution is limited by historical constraints2. Adaptations are often compromised3. Not all evolution is adaptive4. Selection can only edit existing variations