The Evolution of Populations

1. 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 discoveries • Population is the unit of evolution • Natural selection is means of mechanism • Gradualism: large changes evolve from small changes over long period of time.

2. Genotype Frequencies Population: Localized group of individuals belonging to the same species. Species: Individuals that have the potential to interbreed and 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 in all individuals of the population Diploid, locus, fixed pop., Individuals are selected but Populations evolve.

3. 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 • How many copies of the gene are there in the population? • How many genes are dominant? Recessive? • What are the percentage of each 1000 genes 800 dominant 200 recessive 80%....20%

4. Hardy-Weinberg Theorem Frequencies of alleles and genotypes in a population’s gene pool remains constant over the generations unless acted upon by other agents. The number of times an allele occurs within a population. p= frequency of dominant allele q= frequency of recessive allele p+q=1

5. Hardy Weinberg Equation p2 + 2pq + q2 = 1 Frequency of AA genotype Frequency of Aa +aA genotype Frequency of aa genotype • PKU: recessive allele disease 1 in 10,000 births (q2=0.0001) • What percentage of US population are carriers?

6. 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.

7. You Solve • Allele Frequency of B is 0.7, what would the frequency of heterozygotes by if in HW equilibrium? Frequency of recessive allele? • 313 out of 1432 individuals have a recessive disorder. What percentage of this population are carriers? • 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.

8. Microevolution Changes of the gene pool of a population at the smallest level. Frequencies of Allele in a population. 5 Conditions needed for HW Eq. • Very Large Populations: • Isolation from other populations • No Net Mutations • Random Mating • No Natural Selection A deviation from HW eq. in a gene pool signifies evolution Natural Population are not EXPECTED to be in HW eq.

9. 5 Agents of Microevolution 1. Genetic Drift: changes in the gene pool of a small population

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

11. Cause of Microevolution Cont. • Gene Flow: genetic exchange due to alleles migrating in or out of a population. Will tend to reduce differences b/w populations. • Mutations: Change in DNA of an organism. Must occur in gametes, rare occurrence of this occurring.

12. Cause of Microevolution Cont. • Nonrandom Mating: “Inbreeding”; relative frequency of genotypes deviate from H-W. W/ each generation Heterozygote # decreases. Assortive Mating: selecting partners with similar characteristics. • Natural Selection: differential success of reproduction. Most likely agent to cause microevolution. Selects favorable genotypes

13. 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).

14. Variation Between Populations • Geographical Variations: differences b/w pop (or w/i). due to environmental factors. Natural selection and genetic drift can cause. • Cline: graded change in a trait along a geographic axis.

15. Mutations generate Genetic Variations • Mutation: • Point mutations mostly harmless, occur in somatic cells. Rarely will cause mutant allele allowing for better reproduction success. • Chromosomal Mutation: disrupts development may have benefits. • Bacteria: reproduce every 20 minutes, mutation in one may produce millions in an hour. Antibiotic resistant bacteria

16. Natural Selection as a means of Evolution • Darwinian Fitness: the measure that is critical to selection, is the relative contribution an individual makes to the gene pool of the next generation. • Relative Fitness: contribution of a genotype to the next generation compared to another. Based as a % based on best reproductive member (1).

17. Modes of Selections • Diversifying Selection: environmental factors favors extreme individuals at both ends. • Directional Selection: changes that occur when moving to new area with different conditions. • Stabilizing Selection: cuts extreme varients, reduce phenotypic variation, status quo

18. Natural Selection and Perfection Natural Selection cannot produce perfection WHY??? • Evolution is limited by historical constraints • Adaptations are often compromised • Not all evolution is adaptive • Selection can only edit existing variations