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Unformatted text preview: Co-dominance: heterzygote shows phenotypes of both alleles fully/equalIncomplete dominance: two alleles of heterzygote interact resulting in intermediate phenotypeForward geneticsobserved phenotype then look for causal genetic differencesBegins with observed variation in phenotypeLooking for patterns of inheritance in descendents of crosses b/t individuals w/different phenotypesPrimary purpose: to find the normal pathway of metabolism and development by looking at mutantsI)Mutations are individually mappedII)Making crosses b/t strains puts mutations in different combinationsIII)Characterize DNA of different variants (alleles) of genes and explain from variant DNA sequences the differences in structure, function, amounts, and localization within the organism of the metabolically active moleculesReverse Genetics: normal DNAcreate mutationanalyze function of DNA sequence by observation of phenotypic changes. Advantage: large number of mutations of specific kinds can be madeSouthern Blotprobing for specific DNANorthern blotprobing for a specific RNATo determine if a gene is being transcribed in a tissueWestern blotprobing for a specific protein Usually formed with antibodies Developmental noise--Random events in development that lead to variation in phenotype Mendels law of equal segregation--in meiosis, the members of a gene pair separate equally into eggs and spermSINGLE GENE INHERITANCE1:1 for Y/y x y/y 3:1 for Y/Y x Y/y1:2:1 for Y/y x Y/yPHENOTYPIC RATIONSMonohybrid test-crossed: 1:1Monohybrid selfed: 3:1Dihybrid testcrossed (ind. Ass.): 1:1:1:1Dihybrid selfed (ind. Ass): 9:3:3:1Trihybrid test-crossed (ind.): 1:1:1:1:1:1:1:1GENE INTERACTIONS9:7 ratiogenes in same pathwayDouble mutant has same phenotypes as two single mutantsEach mutant allele controls different step in same pathwayCan also come from gene regulationoRegulatory gene produces protein that binds to regulatory stream upstream of target geneoTarget gene would be transcribed at low levelsAbsence of either gene function leads to absence of end product of the pathway9:3:4 ratiorecessive epistasis Double mutant shows phenotype of one mutation but not otheroEpistaticoverriding mutationoHypostaticoverridden mutationResults from genes in same pathwayEpistatic mutation is in gene upstream of overridden oneCan be developmentally downstreamTypically 3 phenotypes segregate12:3:1 ratiodominant epistasisSuppressormutant allele that reverses effect of mutation of another gene, results in wild-type or near wild-type phenotypeGene products normally interactSometimes have no effect in absence of other mutation or can produce own abnormal phenotypeScreeningExpose mutant to mutation-causing agentsScreen for wild-type descendentsoMost will by revertants (reversals of org. mutational event)oSome will be pseudorevertantsdouble mutants w/one being...
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This note was uploaded on 04/01/2008 for the course ZOL 341 taught by Professor Dworkin during the Spring '08 term at Michigan State University.
- Spring '08