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6/15/2016 Lecture 7 Microevolution Microevolution 1. 2. 3. 4. 5. What causes evolution? Allele frequencies: A critical measure Gene flow Non-random mating Genetic drift What is an allele frequency? Population = a group of individuals from a single species Genes are all the same, but alleles probably differ Mutations 1. 2. 3. 4. 5. How do codons get read? Incorrect readings: a variety of point mutations Chromosome level mutations Aneuploidy and polyploidy Causes and effects of mutations Microevolution What is an allele frequency? Allele frequency is simply the number of times an allele occurs in the population. Frequencies are represented as a proportion of the whole (typically in decimal form). Tongue rolling: Ability to roll = RR or Rr Inability to roll = rr Microevolution How do allele frequencies change? 1. 2. 3. 4. 5. Gene flow Non-random mating Genetic drift Mutation Selection 1 6/15/2016 Microevolution Microevolution Gene flow Gene flow Microevolution Microevolution Non random mating Non random mating Assortative mating: Organisms of similar phenotype mate more often than expected by random chance Tends to increase the frequency of homozygotes in the population 2 6/15/2016 Microevolution Non random mating Microevolution Genetic Drift Microevolution Genetic Drift Microevolution Genetic Drift Drift is all about sample size! 3 6/15/2016 Microevolution Mutations Mutation RNA codes for particular amino acids Mutation is the ultimate source of all genetic variability Mutations Mutations The codes for amino acids are degenerate Francis Crick and Sydney Brenner determine how codons are read 4 6/15/2016 Mutations Deletion only disturbs one word Mutations Single or double deletions Mutations Deletion skews all “downstream” words Mutations Triple deletions 5 6/15/2016 Mutations C AUGUAUGCUCCGAAU Mutations * Codons are read in threes * Codons are not spaced * Reading frame is critical AUGAUGCUCCGAAU__ AUGCUAUGCUCCGAAU Francis Crick and Sydney Brenner Frameshift mutation via addition Mutations Orig seq = TACACCGAGGGCCTAATT Mutations Orig seq = TACACCGAGGGCCTAATT 6 6/15/2016 Mutations Orig seq = TACACCGAGGGCCTAATT Mutations Frameshifts Silent muations Point mutations Missense Nonsense Mutations Mutations Also see Life 10e Fig 15.4 7 6/15/2016 Mutations Mutations Also see Life 10e Fig 15.4 Mutations Also see Life 10e Fig 15.4 Mutations Meiosis 1 (the first division) Nondisjunction: occurs when chromosomes fail to separate during Metaphase 1 Normal meiosis: Chromosomes have regular disjunction and separate into daughter cells Aneuploids: have gained or lost a chromosome Also see Life 10e Fig 15.4 8 6/15/2016 Mutations Mutations 22 22 23 23 Monozomy Monozomy Mutations Mutations Chromosomes 13, 15, 18, 21, 22 can be doubled and lead to individuals that survive for a time 23 24 Trizomy Normal karyotype 9 6/15/2016 Mutations Trisomy 21 karyotype Mutations Aneuploidy is very common in sex chromosomes Mutations Mutations Ploidy = number of copies of chromosomes Aneuploidy is thought to be very common More than two copies = polyploid (xN) Banana plants come in many ploidy levels: 2N= 22 4N = 44 5N = 55 7N = 77 10 6/15/2016 Mutations Mutations Four causes: * Ionizing radiation * Chemical mutagens * Exposure to some viruses * Spontaneous mutation during replication Mutations Three outcomes: * Beneficial * Harmful * Neutral * Beneficial Mutations Lethal * Harmful * Neutral Three outcomes: Three outcomes: * Harmful Minor to major effects * Neutral Silent Non-coding * Beneficial No fitness loss 11 6/15/2016 Mutations Three outcomes: * Harmful * Neutral * Beneficial Natural selection Lecture 8 Natural Selection 1. 2. 3. 4. 5. 6. The only adaptive evolutionary force Stabilizing selection Directional selection Disruptive selection Balancing selection Determining fitness Sexual selection 1. 2. 3. 4. 5. Males and females have different reproductive strategies Females choose… …most of the time (when the exception proves the rule) Males compete Females gain by their choosiness a. Co-parents b. Territory c. When males don’t stick around – theories! Natural selection Grant and Grant Can you think of an example of a bottleneck event that we’ve already discussed in class? Did the finches go through a bottleneck? Did genetic drift change their beak size? from P. T. Boag and P. R. Grant in Science 214:82, 1981 12 6/15/2016 Natural selection Natural selection What force changed the finch’s beaks? Factors required for natural selection to operate: 1. There must be variation in the population 2. Variation must lead to differences among individuals in lifetime reproductive success 3. Variation must be transmitted to the next generation Natural selection Natural selection Factors required for natural selection to operate: 1. There must be variation in the population 2. Variation must lead to differences among individuals in lifetime reproductive success Generation 1 3. Variation must be transmitted to the next generation 13 6/15/2016 Natural selection Selection is the only adaptive evolutionary force Natural selection Common selective forces: 1. 2. 3. 4. 5. 6. But what can adapt? Natural selection Predation is a strong selective force Predation Climatic factors Parasitism Mate attraction Resource acquisition More! Natural selection Predation is a strong selective force 14 6/15/2016 Natural selection Natural selection Absolute fitness Relative fitness Relative fitness = 3/3 or 1 Fitness = 3 Generation 1 Generation 1 Relative fitness = 1/3 or .33 Fitness = 1 Natural selection Stabilizing selection Natural selection Directional selection Bella coola Directional selection by fishing on pink salmon Onchorhynchus gorbuscha 15 6/15/2016 Natural selection Natural selection There’s one other type of selection: Balancing selection Disruptive selection Agrostis tenuis Mine Index of tolerance Nonmine soil 1. Heterozygote advantage 2. Negative frequency dependent selection 0 50 100 150 Distance in meters Natural selection Natural selection Balancing selection Heterozygote advantage Balancing selection Negative frequency dependent selection Relative fitness AA - .75 Aa – 1 aa - .25 A sickled blood cell Relative fitness Common .65 Rare 1 16 6/15/2016 Natural selection Balancing selection question: Sexual selection Sexual selection Evolution is all about mating Sexual selection 17 6/15/2016 Sexual selection Reproductive Strategy Mate choice Mating frequency Mate guarding Long-term mating behavior (monogamy vs. polygyny) Parental care Offspring spacing Sexual selection Females are choosy! Sexual selection Darwin notes: Females often do not mate with the first male they see. They evaluate. Sexual selection Energy Human eggs are 195,000X larger than sperm and contain far more nutrients. 18 6/15/2016 Sexual selection Sexual selection Time Purely mathematical Females cannot have as many offspring as males Gestation limits new mating opportunities Maternal care takes time Sexual selection Sexual selection Take home message: For males, sex is cheap. For females, the after effects can be VERY costly. Take home message: For males, sex is cheap. For females, the after effects can be VERY costly. Sexes differ in parental investment 19 6/15/2016 Sexual selection Sexual selection Some males stick around! So if females choose, what do males do? Sexual selection Male riflebird Female riflebird http://news.nationalgeographic.com/news/2007/02/070221-riflebird-video.html 20 6/15/2016 Sexual selection Sexual selection Sexual dimorphism What are the females getting by being choosy? Good dads Sexual selection Sexual selection What are the females getting by being choosy? What about absent fathers? Resource protection 21 6/15/2016 Sexual selection Sexual selection 1. Oldest 2. Largest 3. Healthiest GOOD GENES Handicap principle Sexual selection Sexual selection Runaway selection Runaway selection 22 6/15/2016 Sexual selection Natural selection will slow runaway sexual selection 23