1. Chapter 17 Evolution of Populations

2. 17.1 Genes & Variation A.Evolution & Genetics 1.Natural Selection acts directly on phenotype (characteristics), not genotype (alleles) a.Why? B/c it is an entire organism- not a single gene- that either survives and reproduces or dies without reproducing

3. 2. Populations & Gene Pools a.population: a group of individuals of the same species that can mate & produce offspring b.The gene pool for a population consists of all the genes that are present in the population c.The relative frequency of an allele is the # of times the allele occurs in the gene pool d. Evolution is any change in the relative frequency of alleles in a gene pool of a population over time.

4. Relative Frequency of Alleles Sample Population 48% heterozygous black 36% homozygous brown 16% homozygous black Frequency of Alleles allele for brown fur allele for black fur Section 16-1

5. B.Sources of Genetic Variation 1.Mutations a.In a single gene or b. large pieces of a chromosome c.Neutral mutations: do not affect phenotype d.If the phenotype is affected, the fitness may or may not be affected -Cause genetic disease (lethal) -Decrease ability to survive & reproduce -May improve ability to survive & reproduce (adaptation) e. matter if they can be passed on in the next generation (egg & sperm cells) f. Ex: UV, radiation, tobacco, toxins, spontaneous mutations (very rare)

7. 2. Sexual Reproduction a. most genetic differences are due to genetic recombination in S.R. b. Crossing over in prophase I of meiosis c. “descent with modification”

8. 3. Lateral Gene Transfer a. passing genes from one individual to another (not offspring) b. Can occur between same or different species c. ex: bacteria & antibiotic resistance

9. Exercise your biology muscle by building your QUADS! 17.1 QUAD How does sexual reproduction affect a population’s genetic variation?

10. C. Single Gene & Polygenic Traits 1.Single Gene Traits a.Trait controlled by only 1 gene  2 alleles (R & r) b.Complete dominant & recessive trait c.2 or 3 distinct phenotypes

11. Frequency of Phenotype (%) 100 80 60 40 20 0 Attached Earlobes (ff) Free Earlobes (FF, Ff) Phenotype Phenotypes for Single-Gene Trait

12. 2. Polygenic Traits a.Many human traits (height, weight, hair color, skin color, eye color) b.Controlled by 2 or more genes that have 2 or more alleles c.Wide range of phenotypes d.Graph of phenotypes is a bell curve  normal distribution e.Average phenotype is most common

14. 17.2 Change in population A.Natural Selection 1.N.S. in single gene traits a.Leads to changes in allele frequencies  Causes changes in phenotypic frequencies b.Ex. Red lizards are more visible to predators and therefore, may be more likely to be eaten and not pass on that red gene. - Black lizards can warm up faster and feed more so they can move away from predators  produce more offspring than brown lizards

16. 2. N.S. in polygenic traits a.Directional Selection -One end of curve has higher fitness -Entire range shifts to right or left -One extreme is lost, one extreme is favored

17. b. Stabilizing Selection - individuals near center (average) are favored - lose extreme phenotypes - ex. Human birth weights c. Disruptive Selection - individuals at end of curve (extreme phenotypes) are favored - average phenotype is reduced

18. B. Genetic Drift 1. Bottle Neck a. The population gets quickly reduced by a natural disaster b. Causes a change in allele frequencies  reduces genetic diversity

19. 2. The Founder Effect a. Genetic drift that occurs when a few members of the population leave and colonize a new habitat b. the new population will have a different allele frequency b/c there are less individuals in the population

21. C. Genetic Equilibrium 1. Hardy Weinberg: allele frequencies will remain constant unless one or more factors causes the frequencies to change. a. large population b. no mutation c. random mating d. no immigration e. no natural selection 2. we study how populations change by determining what is necessary for no change to occur

22. 3. Hardy- Weinberg Equations p 2 + 2pq + q 2 =1 p 2 = frequency of AA 2pq = frequency of Aa 100 % of population q 2 = frequency of aa p + q = 1 p = frequency of A q = frequency of a ***Round to the thousandths

23. In a population of flowers, 36 are homozygous dominant, 48 are heterozygous and 16 are homozygous recessive. – What is the frequency of the organisms in the population that are DD? 36/100 = 0.36 DD (p 2 ) – What is the frequency of the organisms in the population that are dd? 16/100 = 0.16 dd (q 2 ) – What is the frequency of the dominant allele? (p) (HINT: find p 2 1 st, then solve for p) 36/100 = 0.36 p 2 p = 0.6

24. In a population of snails, 45 have narrow shells and 455 have rounded shells. Round shell is completely dominant over narrow shells. – What is the frequency of the dominant allele? (HINT: solve for q 2 1 st, then q, then p) 45/500 =0.09 = q 2 (aa) q= 0.3 p= 1-0.3 = 0.7 – What is the frequency of the heterozygotes? 2pq = 2(0.3)(0.7) = 0.42 Aa – What is the frequency of AA? p 2 = (0.7) 2 = 0.49

25. 17.3 Speciation- How do we get new species? A. What is a Species? 1. Species: a group of interbreeding organisms that breed with one another and produce fertile offspring. a. This means that the individuals of the same species share a common gene pool.

26. 2. If a beneficial genetic change occurs in one individual, then that gene can be spread through the population as that individual and its offspring reproduce.

27. B. Isolating Mechanisms (Leads to a new species!) Reproductive Isolation – members of two populations cannot interbreed and produce fertile offspring.

28. 1. PRE-Mating Reproductive Isolation – involves mechanisms which do not allow mating to occur in the first place. a. Behavioral Isolation: Members of two populations are capable of interbreeding but have differences in mating displays or courtship rituals. - Specific scents- pheremones - Color pattern/ strutting - Specific calls or sounds

29. b. Geographic/Ecological Isolation: Two populations are separated by geographic barriers such as rivers, mountains, or bodies of water.

30. c. Temporal Isolation: Two or more species live in the same habitat but have different mating/reproductive seasons. Examples - Brown trout and Rainbow trout are found in the same streams but Rainbow trout spawn in the Spring and Brown trout spawn in the Fall. - Three similar species of orchid living in the same tropical habitat each release pollen on different days

31. 2. POST-Mating Reproductive Isolation – (fertilization occurred and zygote formed) a. Hybrid inviability: hybrid zygotes fail to develop or fail to reach sexual maturity. b. Hybrid sterility: Hybrids fail to produce functional gametes. Example: horse x donkey => mule (sterile).