Lecture 7 Outline of Last Lecture I. MendelII. Mutations Outline of Current Lecture I. How can allele frequency change?-Review of mutations-Natural selection -Directional selection-Stabilizing selectionExamples:Anthro 1031st editionPeppered mothsGalapagos finchesSickle-cellCurrent LectureHow can allele frequency change?1. Mutation2. Natural selection3. Gene flow4. Genetic driftMutation:-randomThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best-point mutations - "frame shifts" - single nucleotide is changed (AT, GC)Deletion: lose a GC, everything is shifted up in the order (goes from ATGA to ATA on one side and TACT to TAT on other side)Insertion: Opposite of delection. Have GC added to order (goesfrom ATA to ATGA)Analogy: Substitution: The Cat Saw the Dog - Can make a point mu-tation, changing sentence to The Bat Saw the DogDeletion: Take out C in The Cat Saw The Dog -> The ATS AWT HED OG (loss of C shifts everything up one)-chromosomal-harmful, neutral, beneficial-gametes-environmental - mutagensNatural Selection:Common examples:-peppered mothHas 2 phenotypes, black and white. Black moths are morerare than white.These phenotypes are pre-existing variationMoths land on trees, the white ones become almost invis-ible compared to the black ones that stick out clearly to predators.When black allele shows up in offspring, it is more likely to die because it is more visible so natural selection re-sults in there being more white moths.Then, soot from Industrial Revolution covers trees and makes the bark dark. Now the black moth has an advan-tage and the white moths are at a disadvantage. Frequency of black allele becomes greater as white allele frequency be-comes lesser."Fitness is relative" - No such thing as absolute fitness, depends on the environment (white moth had the most fitness until the environment changed)No traits are absolutely good. They're relative to the environment.-galapagos finchesDarwin was interested how finches were similar but dif-ferent from the ones he knew.Couple (Peter and Rosemary Grant) studies finches on one island, Daphne Major.Medium ground finch - one speciesBeak is short, good for eating seedsCouple captured all 1500 birds on the islandMeasured beak sizepre-existing variationheritableWeather - how much rainfall today, tomorrow?What is the humidity?Day/Night time temperatureFood availabilityHow many seeds were available for birds to eat?Counted all seeds in 1 meter by 1 meter squareSeed sizeHardness/softness of seedsHow big/small are the seedsThere was a drought and plants that produced seeds dried outFindings:Number of seeds declinedNumber of birds declined (Malthus' "struggle for existence")1400 birds reduced to 200 birdsWho survived? Was it random?Shallow beak birds had low survivalBig beak birds had higher probability of survivalWhy did big-beaked birds survive?All birds ate the small seeds available, and once those were gone, hard seeds were left. Big-beaked birds were able to eat the hard seeds.'Directional' selection: change going from small beaks to big beaksDirection is not permanent. Changing environment changes se-lective pressure. White moths may become predominantly black, but with another environmental change, they can go back to beingwhite moths. (Note: Individuals don't change, populations do. Single white moth can't become a black moth, but over time the majority of the popu-lation can change from predominantly white to predominantly black)Natural selection:-Directional selection-Stabilizing selectionWhen humans were developing and brains became big-ger, it was harder to push bigger-headed babies through birth canalEx: larger and smaller babies were less likely to survive (big babies because they were harder to get through birth canal and small babies because they were underdeveloped)Eventually baby size becomes an average weight, stabiliz-ing-sickle cell disease in humansBlood disease - hemoglobinRed blood cells supply oxygen around the bodySickle cell shape clogs pathwaysHow can a serious disease be favored by natural selection?Two alleles for sickle cell - codominanceAA = normal hemoglobinAS = both expressed (sickle-cell trait)SS = sickle-cell diseaseThose with sickle-cell trait may be fine, they also may have symptomsPeople with SS tend not to reproduce so allele becomes lesser in the populationFitness is relative!Certain spots of the world have higher frequency of S allelePrevalence of malaria tied with sickle-cell alleleIf you live somewhere with malaria and have sickle-cell geno-type (AS), you have resistance to malariaNote: People with SS in malaria area will have sickle-cell dis-ease and will get malaria, although they are better off for