Topic 09 Evolution. I. Populations A. Evolution is change over time. (change in the frequency of heritable phenotypes & the alleles that govern them)

Transcription

1 Topic 09 Evolution I. Populations A. Evolution is change over time (change in the frequency of heritable phenotypes & the alleles that govern them) I. Populations A. Evolution is change over time (change in the frequency of heritable phenotypes & the alleles that govern them) B. Populations are the units of evolution 1

2 I. Populations A. Evolution is change over time B. Populations are the units of evolution Microevolution detected here Allelic and phenotypic freq. change in pops. Contrast with macroevolution. Macroevolutionary phenomena include: 1. Speciation 2. Extinction 3. Transitions from water to land, etc. a. When & How: 1) Mitotic or meiotic DNA Replication errors 2) Recombination errors (meiosis) 3) Natural accidents or induction by mutagens 2

3 a. When & How: 1) Mitotic or meiotic DNA Replication errors 2) Recombination errors (meiosis) 3) Natural accidents or induction by mutagens b. Types: a. When & How: 1) Mitotic or meiotic DNA Replication errors 2) Recombination errors (meiosis) 3) Natural accidents or induction by mutagens b. Types: 1) Base substitutions. In protein coding genes, such mutations can be a.) Silent mutations b.) Missense mutations c.) Nonsense mutations Silent Wildtype mrna mrna 5 -AUCGAUGAAGUUAAUGGCAUGA-3 protein Met Lys Leu Met Ala Mutant mrna 5 -AUCGAUGAAAUUAAUGGCAUGA-3 protein Met Lys Leu Met Ala 3

4 Silent Missense Wildtype mrna mrna 5 -AUCGAUGAAGUUAAUGGCAUGA-3 protein protein Met Lys Leu Met Ala Mutant mrna 5 -AUCGAUGAGGUUAAUGGCAUGA-3 protein Met Arg Leu Met Ala Silent Missense Nonsense Wildtype mrna mrna 5 -AUCGAUGAAGUUAAUGGCAUGA-3 protein protein Met Lys Leu Met Ala Mutant mrna 5 -AUCGAUGAAGUAAAUGGCAUGA-3 protein Met Lys a. When & How: 1) Mitotic or meiotic DNA Replication errors 2) Recombination errors (meiosis) 3) Natural accidents or induction by mutagens b. Types: 1) Base substitutions a.) Silent b.) Missense c.) Nonsense 2) INDELS a) Insertions b) Deletions 4

5 Insertions Wildtype mrna mrna 5 -AUCGAUGAAGUUAAUGGCAUGA C inserted Mutant mrna 5 -AUCGAUGAAGUUAACUGGCAUGA protein protein Met Lys Leu Met Ala Met Lys Leu Thr Gly Met Iso Deletions Wildtype mrna mrna 5 -AUCGAUGAAGUUAAUGGCAUGA G lost Mutant mrna 5 -AUCGAUGAAGUUAAUGCAUGA protein protein Met Lys Leu Met Ala Met Lys Leu Met His Asp Deletions Wildtype mrna mrna 5 -AUCGAUGAAGUUAAUGGCAUGA protein Met Lys Leu Met Ala G lost Mutant -INDELS in protein coding mrna genes 5 -AUCGAUGAAGUUAAUGCAUGA shift the reading frame protein Met Lys Leu Met His Asp 5

6 a. When & How: b. Types: c. Effect: Drosophila research: 70% deleterious 30% neutral or weakly advantageous 2. Genetic drift Chance-driven changes in trait frequencies. Occurs more rapidly in small populations Scenario 1: Chance failure of an individual(s) of one phenotype to reproduce Counts (Frequencies) Phenotype Gen 0 Gen 1 Purple 9 (0.75) 8 (0.73) Green 3 (0.25) 3 (0.27) Chance death or failure to mate of one individual Simple assumptions for this example: each individual replacing itself and complete turnover from one generation to another. 6

7 Scenario 1: Chance failure of an individual(s) of one phenotype to reproduce Smaller Population Counts (Frequencies) Phenotype Gen 0 Gen 1 Purple 3 (0.75) 2 (0.67) Green 1 (0.25) 1 (0.33) Chance death or failure to mate of one individual Scenario 1: Chance failure of an individual(s) of one phenotype to reproduce Smaller Population Counts (Frequencies) Phenotype Gen 0 Gen 1 Purple 3 (0.75) 3 (1.00) Green 1 (0.25) 0 (0.00) Chance death or failure to mate of one individual Scenario 2: Chance mutation followed by drift 7

8 Scenario 2: Chance mutation followed by drift Smaller Population Counts (Frequencies) Phenotype Gen 0 Gen 1 Gen 2 Purple 3 (0.75) 2 (0.50) 1 (0.25) Green 1 (0.25) 1 (0.25) 1 (0.25) White *1 (0.25) 2 (0.5) mutation introduces new Chance reproduction fluctuations Scenario 2: Chance mutation followed by drift Larger Population 2. Genetic Drift 3. Nonrandom Mating -when prob. of one indiv. mating w/ another in pop. is not random. 8

9 2. Genetic Drift 3. Nonrandom Mating a. At organismal level e.g. geographical proximity has big influence on mating 2. Genetic Drift 3. Nonrandom Mating b. w/ respect to individual traits e.g. in humans, mating may be random w/ respect to handedness But likely non-random w/ respect to others (this is called sexual selection) e.g. Male frog croaking Force air through larynx, but vocal sacs amplify. Species-specific Which means its selected for. 9

10 Experimental proof that croak volume is selected for Experimental proof that the sound of a croak is maintained via sexual selection Male peafowl (peacock) plumage Displayed prominently during courtship Fitness benefits Attraction of peahens Fitness Costs Increase metabolic cost Increased visibility & decreased flight speed in relation to predators? 10

11 Artificial selection (selective breeding) is human-induced non-random mating Canis lupus Canis lupus ssp. familiaris Artificial selection (selective breeding) is human-induced non-random mating 2. Genetic Drift 3. Nonrandom mating 4. Migration (gene flow) 11

12 4. Migration Scenario 1 aa AA Population of 4 individuals before f(a) = 0.50 f(a) = Migration Scenario 1 aa emigration AA Population of 4 individuals before f(a) = 0.50 f(a) = Migration Scenario 1 aa Population before f(a) = 0.50 f(a) = 0.50 Population after f(a) = 0.33 f(a) =

13 4. Migration Scenario 2 aa AA Population before f(a) = 0.50 f(a) = Migration Scenario 2 aa AA immigration AA Population before f(a) = 0.50 f(a) = Migration Scenario 2 aa AA AA Population before f(a) = 0.50 f(a) = 0.50 Population after f(a) = 0.60 f(a) =

14 2. Genetic drift 3. Nonrandom mating 4. Migration 5. Natural selection (differential fitness of organisms based on their heritable traits) a. Directional Selection a. Directional Selection b. Stabilizing Selection 14

15 Directional or Stabilizing? To elements involved here: 1. Prexisting variation and new variation in resistance via mutation 2. Natural selection (selective agent: antibiotics) Is this the result of directional or stabilizing? 15

16 Is this the result of directional or stabilizing? Is this the result of directional or stabilizing? 16

17 2. Genetic drift 3. Nonrandom mating 4. Migration 5. Natural selection (differential fitness based on phenotype) a. Directional Selection b. Stabilizing Selection Stabilizing Selection in Humans Weakness causing difficulty eating, low fat content causing difficulty thermoregulating. Delivery complications related to pelvic size, etc. 17