Biol 3350 1st Edition Lecture 8 Outline of Last Lecture I. Dilemma/Critiques for DarwinII. Castle’s ExperimentIII. Maintenance of variationIV. SpeciationV. The Contributions of MendelVI. The Modern SynthesisOutline of Current Lecture I. What is Selection?II. Stabilizing SelectionIII. Directional SelectionIV. Genetic Mutationsa. Point mutationsb. Transitionsc. Transversionsd. Insertions or deletionse. Silent substitutionsf. Missense mutationsg. Nonsense mutationsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.h. Frameshift mutationsV. Mutation RatesVI. Chromosomal MutationsCurrent LectureI. What is Selection?a. Mechanism of evolutionb. Genetic Drift is anotherc. Selection acts on phenotypes and the genes that produce themII. Stabilizing Selectiona. Mice that were too dark on the light environment, had low survival à selection was acting against themb. Selection is stabilizing the representation of coat colors so that it matches the environmentc. Saw that the mechanisms of selection (predation acting against survival) stabilized selectionIII. Directional Selectiona. Selection is acting against one extreme and is changing allele frequencies in the populationb. The environment drives changes in phenotypesc. Ex: if new predator is introduced, the environment is changed, and pressure for adifferent kind of phenotype occursd. Before the drought – variation in beak depthe. After drought – beak depth shifted to a higher value due to the change in the environmentf. Change in the mean value of the traits shows that selection has occurred à the mean is higher, which means directional selection has occurredg. Force of selection is driving towards larger beaksIV. Genetic Mutationsa. Point mutationsi. Single base pair substitution à point mutationii. DNA has a mechanism that can repair these but sometimes these mechanisms do not work b. Transitionsi. Thymine and Cytosine = Pyramadinesii. Cytosine can be modified by the addition of a methyl group, lose amine group and become thymineiii. Adenine and Guanine = Purinesc. Transversionsi. Transversions are more complicatedii. Transitions have fewer chemical steps à more commond. Insertions or deletionsi. More common for this to be incorporated into the DNA in non-coding regions b/c no dramatic phenotypic changes result (pretty common)ii. Formed by slippageiii. Basis of microsatellite allelesiv. More common in non-coding regionse. Silent substitutionsi. Most of the point mutations that get incorporated are silent mutationsii. Synonymous substitutions because they result in the same amino acidf. Missense mutationsi. These usually occur in the 2nd or 3rd position on the codonii. If change an amino acid in the protein à change shape and function of proteiniii. Sometimes these mutations are beneficial (not usually) and this is how we get new adaptationsiv. Missense – change in nucleotide that causes a change in the amino acid that is producedv. Conservative – produces same type of amino acid (both basic amino acids)vi. Non-conservative – produces a different type of amino acid (ex: basic à polar amino acid); more dramatic changeg. Nonsense mutationsi. Changes in DNA that result in insertion of a premature stop codon into mRNAii. Early stop signaliii. Halts translationiv. Protein is non-functionalh. Frameshift mutationsi. Indel = insertion and deletionii. All codons downstream will be changed so the protein is completely non-functionalV. Mutation Ratesa. Spontaneous mutationsi. Mutations occur by chance at a low frequencyii. Rate varies among genes and among speciesiii. Many alterations to DNA are repaired and do not become persistent mutationsiv. Ex: Drosphila1. Normally has red eyes2. Point mutation on chromosome 2 produces brown eye (recessive)3. Point mutation on X chromosome causes white eyes (recessive)b. Recurrent Mutationsi. Mutations that occur by chanceii. Higher in mammals that have shorter generations and reproduce fasteriii. Albinism in micec. Inducted mutationsi. Mutagens are substances that increase the mutation rate above the spontaneous rate1. UV light à skin cancer2. Most mutations are deleterious or even lethald. Mutation is a random eventi. Mutation rates are affected by environmentii. Mutation is not directed with respect to the environmentVI. Chromosomal Mutationsa. Some mutations occur because of major chromosomal mutationsb. Karyotypic – results in big changes in more than one chromosome; changes morethan one genes in the same chromosomei. Polypoidy – more than the origin two sets of chromosomesii. - can come from two different species (allopolypoidy) or from the same species (autopolypoidy)c. Chromosomal mutations – mutation results in changes in more than one gene onthe same chromosomei. Gene duplications1. One chromosome has two copies and other has no copiesii. Unequal crossing over in