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UM BIOB 272 - Natural Selection Adaptation
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BIOB 272 1st Edition Lecture 26Outline of Last Lecture Natural Selection AdaptationI. Directional/stabilizing Selection in HumansII. Case Study 2: Humans and Milk- Selective Sweeps- Haplotype- Convergent and Independent EvolutionIII. Agriculture- artificial selection in crop production - Teosinte and Maize- Kernel StructureOutline of Current Lecture Natural Selection and AdaptationI. Cross-fertile Maize and TeosinteII. Pesticides and Herbicides in SelectionIII. Resistance to Pesticides in HousefliesIV. Key Concepts- Selection in WildV. Adaptationa. Adaptation with Quantitative Charactersb. Complex AdaptationsThese 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.VI. Three Potential Fates of a Duplicated GeneVII. Paralogous Gene vs Orthologous GeneVIII. NeofunctionalizationIX. Case Study: Evolution of Snake VenomsX. Complex Adaptations may involve: - Regulatory NetworkXI. Example of a Regulatory Hierarchy: Hox genesXII. Changes in Limb PatterningXIII. Mutations to Gene NetworksXIV. Key Concepts- AdaptationsCurrent LectureNatural Selection and AdaptationI. Cross-fertile Maize and Teosinte- Maize and Teosinte can cross- fertilize to produce a hybrid offspringParents= Teosinte x MaizeF1= Hybrid OffspringF2= Cross hybrids with each other or one of the parent strains= offspring will have a combination of the characteristics of their grandparents- Are they the same species?o QTL studies indicate that the major phenotypic differences are due to changes at 5 genes (or linked regions)o Many more small genetic changes (perhaps at 1,000s of genes) influence a suite of important traits: starch production, climatesand types of soil, length and number of kernels, kernel size, shape, and color, resistance to pests II. Pesticides and Herbicides in Selection= act as agents of selection- Natural Selection and Evolution- Increasing insecticide resistance threatens pest and disease managementIII. Resistance to Pesticides in Houseflies- A single P450 allele associated with insecticide resistance in Drosophila- -DDT-R, a gene conferring resistance to DDT, isassociated with over transcription of a singlecytochrome P450 gene, Cyp6g1.- Resistance and up-regulation are associatedwith a single Cyp6g1 allele that has spreadthroughout the world.- Increased insecticide resistance can be due to single genes- Rapid evolution of herbicide resistance- Resistance evolves quickly- what can be done?o A potentalsolurton is presented by understanding evoluton&populatongenetcso Resistance often comes at a cost:  Fitness of resistant alleles < 1 when selective agent is not present.  Directonalselecton can be counteracted with refuges. oIV. Key Concepts- Selection in Wild- Artificial selection can have very strong effects on the evolution of plants and animals (including humans) - The signatures of positive selection can be observed with genomic data. - Major phenotypic changes can be caused by relatively few genes, especially when selection is strong. - Resistance in inevitable, but can be counteracted in many cases by applying basic principles of evolution.V. Adaptation: is an inherited trait – or integrated suite of traits –that increases the likelihood that an individual will surviveand reproduce, relative to individuals lacking this trait.a. Adaptation with Quantitative Characters: (most of what we have discussed)= subtle changes in beak size, hair color, etc.b. Complex Adaptations:suites of coexpressed traits that when expressed to together experience selection for a common function. Influenced by many environmental and genetic factors.- Example:o Observation: Many proteins (or networks of proteins)are finely adapted to a particular function.How can a protein (gene) take on a new function?1. Many genes are promiscuous with respect tofunction and may be specialized for multiple differentfunctions.• Alternative splicing is a classic example of how onegene may take on many functions.2. Genes can be duplicated over evolutionary time.VI. Three Potential Fates of a Duplicated Gene:1. Ceases to function (pseudogene)2. One copy evolves new function (neofunctionalization)3. Each copy evolves to specialize on a subset of the originalfunction (subfunctionalization)VII. Paralogous Gene vs Orthologous Genea. Paralogous Gene: homologous genes that arise from a duplication eventb. Orthologous Gene: Homologous genes separated by a speciation eventVIII. Neofunctionalization: major source of evolutionary novelty whereby genes (or networks of genes) are recruited for novel functions.IX. Case Study: Evolution of Snake Venoms- Different species produce distinct cocktail of venoms- Venom genes usually very closely related between species, suggesting common ancestry and descent with modification. - Crotamine (muscle-destroying) snake venoms evolved through neofunctionalization of genes involved in innate immune defense- Repeated recruitment of venom genes through neofunctionalizaiton of genes expressed in other tissuesX. Complex Adaptations may involve: a. Changes in proteins encoded by genesb. Regulatory elements that control the expression of genesc. OR- a mix of both- Regulatory Network- commonly use these for individual genes to function o Systems of interacting gnees, regulatory elements, RNA, and other molecules that function like biological circuitso During development regulatory networks are often strongly hierarchical and modular.XI. Example of a Regulatory Hierarchy: Hox genes- Different regions express different combinations of genes- In flies, Hox genes assign different developmental sections of the body along the anterior to posterior axis to different body partso These genes are expressed in the same order that they occur in the embryoXII. Changes in Limb Patterning: - Expression differences in a single gene give rise to limb elongation= these genes called orthologs- Related set of genes control development in mice= fly legs and mouse legs patterened by same genetic cascade i.e. change in expression of Dpp (in flies) and BMP2 (in bats)- Dispruptions in Shh expression= no limbs and expansion of trunko Fore limb reduction through expansion of anterior Hox expressiono Hind limb reduction through down regulation of ShhXIII. Mutations to Gene Networks- Can produce additional appendages- Ectopic expression of Shh triggers the formation of a new limbXIV. Key Concepts-


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UM BIOB 272 - Natural Selection Adaptation

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