Chapter 17: Processes of Evolution

1. Chapter 17: Processes of Evolution Unit 6: Evolution

2. Case Study: Rise of the Super Rats • Rats are one of the most notorious pests of all time • Cost us about ____________ each year • Rodenticide warfarin: very effective when first used • Rats developed resistance – inherited gene that made the chemical ineffective • This is an example of: __________________________________

3. Variation in Populations • _______________ : one group of individuals of the same species in a specified area • Species share: • Morphological traits • Physiological traits • Behavior traits • Populations show variation in traits: • Qualitative: __________________________ • Quantitative: _________________________

4. The Gene Pool • The genes of a population comprise the _______ ________, a pool of genetic resources • Alleles are the primary source of variation in appearance • Polymorphism: occurs when genes have three or more alleles that persist in a population with a frequency of at least 1% • Example: _______________________ • ________________ : two distinct traits • Example: male / female

5. Mutations • Mutations are the source of new alleles • We can predict average mutation rates • In humans: ________ mutations per person per generation • Many mutations give rise to structural, functional, or behavioral alterations that reduce an individual’s chance of surviving and reproducing

6. Mutations • Mutations can be: • ____________ : usually arise from drastic changes in the phenotype • _____________: alter the base sequence of DNA but have no effect on survival or reproduction • ______________: enhances the survival or reproduction – occurs every so often • Natural selection will favor the transmission of beneficial mutations on to the next generations

7. Stability and Change in Allele Frequencies • Researchers typically track _____________ _________________ in populations (how often a certain allele occurs) • The relative abundance of alleles of a given gene among all individuals of a population • For a starting point, they use a reference called genetic equilibrium, when a population is not evolving with respect to a certain gene • Genetic equilibrium can ONLY be reached when five conditions are met

8. Genetic Equilibrium • Genetic equilibrium can occur only when: • Mutations do not occur • The population is infinitely large • The population stays isolated from all others of the same species • Mating is random • All members of the population survive and produce the same number of offspring • In nature, _______________________________

9. Microevolution • If all 5 conditions are never met, change is occurring within a population • Results in small-scale changes in the population’s allele frequency; called __________________ • Four processes of microevolution: • mutation • natural selection • genetic drift • gene flow

10. When is a population not evolving? • The Hardy-WeinbergFormula can be used to track whether a population is in genetic equilibrium or not • A mathematical formula which tracks allele frequency for a specific trait • Applied rules of probability to sexually reproducing populations and found that the gene pool can only be stable when __________________________ • Researchers can use the formula to estimate the frequency of carriers of alleles that cause genetic traits and disorders

11. Hardy-Weinberg Genetic Equilibrium • Hardy-Weinberg formula: p2 + 2pq + q2 = 1 p + q = 1 where p and q are the frequencies of alleles A and a • You can draw this on a Punnett square:

12. Natural Selection • Natural selection: the differential survival and reproduction among individuals • Natural selection influences all levels of biological organization • Selection can be:

13. Directional Selection • Directional selection occurs when allele frequencies shift in a _____________________ • Forms at one end of the range of phenotypic variations become more common than the intermediate forms • Examples: • Peppered Moth, pocket mice (predation) • Resistance to antibiotics

14. Directional Selection • Butterfly wing color: medium-blue is between two phenotypic extremes (white and dark purple) • Orange arrows identify which forms are being selected against over time Figure 17.5, page 270

15. Peppered Moth • Peppered moth: a classic example of the directional selection process • Feed at night and rest on tree trunks during day • Light gray lichens grew on trees • In preindustrial England, light colored moths were the most common • Due to air pollution starting in 1850s, the dominant allele shifted to dark colored moths • Air pollution was _________________________

16. Peppered Moth • Since the advent of pollution controls starting in 1950s, allele frequency has begun to shift back to light colored moths Figure 17.6, pg 271

17. Pocket Mice • Rock pocket mice in Arizona are another example of directional selection • Light brown granite; dark basalt (lava rock) • Figure 17.7, pg 271

18. Resistance to Antibiotics • Human activity can also influence directional selection • Antibiotics: toxins that kill bacteria by interfering in physiological processes • Since 1940s, have been widely prescribed in the U.S. • Overuse of antibiotics puts tremendous selection pressure on bacteria • Bacteria divide quickly and form huge populations with great genetic variation • E. coli can divide every _________________ • Likely that some will survive antibiotic treatment • Resistant strains are becoming the norm

19. Selection Against or in Favor of Extreme Phenotypes • Stabilizing Selection: works against phenotypes at the fringes of a range • Disruptive Selection: favors phenotypes at the fringes of a range

20. Stabilizing Selection • Stabilizing selection: intermediate forms of a trait in a population are favored • Does NOT _______________________________ • Examples: • Birth weight for babies – mid-sized babies selected for most often • Body mass size of sociable weaver birds • Body mass represents a trade-off between risks of starvation and predation

21. Stabilizing Selection Stabilizing eliminates the ______________ Figure 17.8a, pg 272

22. Disruptive Selection • Disruptive selection: forms at both ends of a range of variation are favored • Intermediate forms are ______________________ • Example: selection for bill size in black-bellied seedcracker finch in Africa • Females and males have either large or small bills (no intermediate ones) • 2 different types of plants: hard or soft seeds • Feeding performance maintains this dimorphism of beak size

23. Disruptive Selection Disruptive selection eliminates _______________________ Figure 17.8b, pg 272

24. Modes of Natural Selection Fig 17.4, page 269