1. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Genes Within Populations Chapter 15 Copyright © McGraw-Hill Companies Permission required for reproduction or display

2. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Gene Variation is Raw Material Evolution is change over time (through several generations).  Darwin - Individuals with desirable characteristics survive and pass on their traits to the next generation - Population gradually includes more individuals with advantageous characteristics. - Species accumulate differences so that ancestral and descendent species are not identical.

3. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Gene Variation is Raw Material Natural Selection and Evolutionary Change  Some individuals in a population possess certain inherited characteristics that play a role in producing more surviving offspring than individuals without those characteristics. - Population gradually includes more individuals with advantageous characteristics.

4. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Gene Variation In Nature Polymorphism  A gene with more than one allele is polymorphic. - Natural populations tend to have more polymorphic genes than can be accounted for by mutation.

5. Hardy-Weinberg Principle Population Genetics - Study of properties of genes in populations.  Blending Inheritance (Phenotypic Inheritance) was widely accepted. - New genetic variants would quickly be diluted.  Meiosis had not yet been discovered. SCIENTISTS COULD NOT ANSWER:  Why don’t recessive traits disappear after a while?

6. Hardy-Weinberg Principle Hardy-Weinberg – Two scientists came up with an explanation at the same time  In 1908, G. H. Hardy and Wilhelm Weinberg independently described a basic principle of population genetics, which is now named the Hardy-Weinberg equation.  Original proportions of genotypes in a population will remain constant from generation to generation.

7. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Hardy-Weinberg Principle Five Assumptions  Population is very large  Mating is random  No mutations  No migration  No selection occurring

8. A herd of horses has one dominant male. All young males are forced to leave the herd. Which of the 5 assumptions is being violated?  A) Population is large  B) Mating is random  C) No mutations  D) No migration  E) No selection

9. A dandelion head full of seeds blows to a secluded valley where there are no others of its kind. The seeds begin a new population. Which of the 5 assumptions is being violated?  A) Population is large  B) Mating is random  C) No mutations  D) No migration  E) No selection

10. A small pride of lions moves into a territory where the dominant male has died. This pride takes in the females of the original pride. Which of the 5 assumptions is being violated?  A) Population is large  B) Mating is random  C) No mutations  D) No migration  E) No selection

11.  A) Population is large  B) Mating is random  C) No mutations  D) No migration  E) No selection In a population of rabbits, there are white and brown phenotypes. The white rabbits are easily seen by predators in the landscape. Which of the 5 assumptions is being violated?

12. Hardy-Weinberg Principle Calculate Genotype Frequencies To find allele frequencies,let: T=frequency of dominant allele t=frequency of recessive allele T + t = 1 (100% of alleles in population) Frequency of homozygous recessive individuals (tt) in the population is: t x t = t 2 Frequency of recessive allele (t) in the population is: t = t 2 Frequency of dominant allele (T) in the population is: T = 1 - t

13. Hardy-Weinberg Equilibrium Copyright © McGraw-Hill Companies Permission required for reproduction or display

14. Five Agents of Evolutionary Change 1. Mutation  Mutation rates are generally so low they have little effect on Hardy-Weinberg proportions of common alleles. - Ultimate source of genetic variation. 2. Gene Flow  Movement of alleles from one population to another. - Tend to homologize allele frequencies.

15. Five Agents of Evolutionary Change 3. Genetic Drift  Frequencies of particular alleles may change by chance alone. - Important in small populations.  Founder Effect - Few individuals found new population (small allelic pool).  Bottleneck Effect - Drastic reduction in population, and gene pool size.

16. Five Agents of Evolutionary Change 4. Selection  Artificial - Breeders exert selection.  Natural - Nature exerts selection. - Variation must exist among individuals. - Variation must result in differences in numbers of viable offspring produced. - Variation must be genetically inherited.  Natural Selection is a process, and Evolution is an outcome.

17. Five Agents of Evolutionary Change Selection Pressures:  Avoiding Predators  Matching Climatic Condition  Pesticide Resistance Copyright © McGraw-Hill Companies Permission required for reproduction or display

18. Evolutionary Forces Maintaining Polymorphism Adaptive Selection Theory  Heterogeneous environments produce many alleles. Neutral Theory  Balance between mutation and genetic drift. Gene Flow versus Natural Selection  Genetic drift may decrease frequency of an allele favored by selection.

19. Heterozygote Advantage Heterozygote Advantage will favor heterozygotes, and maintain both alleles instead of removing less successful alleles from a population.  Sickle Cell Anemia - Homozygotes exhibit severe anemia, have abnormal blood cells, and usually die before reproductive age. - Heterozygotes are less susceptible to malaria.

21. Forms of Selection Disruptive Selection  Selection eliminates intermediate types. Directional Selection  Selection eliminates one extreme from a phenotypic array. Stabilizing Selection  Selection acts to eliminate both extremes. - Fitness - Number of surviving offspring passed to the next generation.

22. Types of Natural Selection

23. In a population of lizards, there are small, medium, and large sized individuals. A food shortage occurs and all of the large sized lizards die of starvation. Which type of selection is occurring? A. Stabilizing selection B. Directional selection C. Disruptive selection

24. Limits to Selection Evolution Requires Genetic Variation  Intense selection may remove variation from a population at a rate greater than mutation can replenish. - Thoroughbred Horses are highly inbred

25. Limits to Selection Selection Against Rare Alleles  As selection only operates on phenotypes, rare recessives cannot be effectively selected against except in homozygote form. - Hardy-Weinberg can still apply even though mutations occur

26. Copyright © McGraw-Hill Companies Permission required for reproduction or display