Cheat Sheet Quiz 2 - Co-dominance heterzygote shows...

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Co-dominance: heterzygote shows phenotypes of both alleles fully/equal Incomplete dominance: two alleles of heterzygote interact resulting in intermediate phenotype PHENOTYPIC RATIOS Monohybrid test-crossed: 1:1 Monohybrid selfed: 3:1 Dihybrid testcrossed (ind. Ass.): 1:1:1:1 Dihybrid selfed (ind. Ass): 9:3:3:1 Trihybrid test-crossed (ind.): 1:1:1:1:1:1:1:1 GENE INTERACTIONS 9:7 ratio—genes in same pathway Double mutant has same phenotypes as two single mutants Each mutant allele controls different step in same pathway Regulatory gene produces protein that binds to regulatory stream upstream of target gene, Target gene would be transcribed at low levels Absence of either gene function leads to absence of end product of the pathway 9:3:4 ratio—recessive epistasis Double mutant shows phenotype of one mutation but not other. Epistatic —overriding mutation (upstr.), Hypostatic—overridden mutation Results from genes in same pathway Typically 3 phenotypes segregate 12:3:1 ratio—dominant epistasis Suppressor—mutant allele that reverses effect of mutation of another gene, results in wild-type or near wild-type phenotype Gene products normally interact Sometimes have no effect in absence of other mutation or can produce own abnormal phenotype In diploids, show different F 2 ratios (13 normal : 3abnormal) Only two phenotypes segregate Modifiers—mutation at second locus that changes degree of expression of mutated gene at 1 st locus Can down-regulate or up-regulate transcription of gene Appearance of two grades of mutant phenotypes within mutant progeny 9:3:3—synthetic lethals—double mutants are lethal MAPPING BY RECOMBINANT FREQUENCY Count # of recombinants for two loci at a time Should double-count double-recombinants Two at high frequency Two at intermediate frequency Two at a different intermediate frequency Two rare—typically double-recombinant classes Chi-squared (Χ 2 ) test —check ratios against expectations To make judgment of whether observed #s are close enough to the expected X 2 =Σ(Observed-Expected) 2 /Expected for all classes Degrees of freedom=number of independent variables in the data=number of genes-1 Null hypothesis: no linkage—independent assortment or due to chance, reject if >5%, p<5% maybe linkage df=(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) Bacteria— circular chromosome and plasmids Prototrophic —wild type, can grow and divide on minimal media Auxotrophic —cells wont grow unless medium contains one or more specific cellular building blocks Conjugation : physical contact and fusion of two different cells. Fertility factor determines if donor or recipient—Hfr 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 outlooping Endogenote
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