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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 phenotypePHENOTYPIC RATIOSMonohybrid 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 pathwayRegulatory gene produces protein that binds to regulatory stream upstream of target gene, Target 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 other. Epistaticoverriding mutation (upstr.), Hypostaticoverridden mutationResults from genes in same pathwayTypically 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 phenotypeIn diploids, show different F2ratios (13 normal : 3abnormal)Only two phenotypes segregateModifiersmutation at second locus that changes degree of expression of mutated gene at 1stlocusCan down-regulate or up-regulate transcription of geneAppearance of two grades of mutant phenotypes within mutant progeny9:3:3synthetic lethalsdouble mutants are lethalMAPPING BY RECOMBINANT FREQUENCY Count # of recombinants for two loci at a time Should double-count double-recombinants Two at high frequencyTwo at intermediate frequencyTwo at a different intermediate frequencyTwo raretypically double-recombinant classesChi-squared (2) testcheck ratios against expectationsTo make judgment of whether observed #s are close enough to the expectedX2=(Observed-Expected)2/Expected for all classesDegrees of freedom=number of independent variables in the data=number of genes-1Null hypothesis: no linkageindependent assortment or due to chance, reject if >5%, p<5% maybe linkagedf=(number of classes in rows-1)x(number of classes in columns-1)Interference (I)=1-(observed frequency or # of double recombinants/expected frequency or # of double recombinants)Bacteriacircular chromosome and plasmidsPrototrophicwild type, can grow and divide on minimal mediaAuxotrophiccells wont grow unless medium contains one or more specific cellular building blocksConjugation: physical contact and fusion of two different cells. Fertility factor determines if donor or recipientHfr is integrated in chromosome, F+is a free plasmid, in an F-cell there is no fertility factor, and F is a plasmid that contains some of chromosome because of faulty outloopingEndogenote(one complete genome of the recipient) and the...
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- Spring '08