PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Friday, September 6, 2013Top 4 for todayEpistasis1)recessive epistasis2) dominant epistasis3) complementary gene action4)novel phenotypesTricks for epistasis – look for familiar ratios (16ths!), and realize it is a single phenotype.Mastering problems will help!Quiz Friday, September 6, 2013Eye color in Drosophila is produced by the recessive, autosomal, unlinked brown and scarlet loci. When both loci are homozygous recessive, no pigment is produced and the eyes are white. If the scarlet locus is homozygous recessive the eyes are bright scarlet, if the brown is homozygous recessive the eyes are a dark brown, and if there is a dominant allele at each locus the eyes are the wildtype brick red.Predict the F1 and F2 results of the following P1 crosses:wildtype x whitebrown x whiteEpistasis OverviewEpistasis – Greek “stoppage”•Intergenic interactions – 2 or more genes interact to effect a SINGLE phenotype•When the effect of one gene or gene pair masks or modifies the effect of another gene or gene pairEpistasis Overview•Many potential interactions:•Antagonistic – e.g. presence of homozygous recessive at one locus (epistatic) prevents expression of other alleles at second locus (hypostatic – masked)•Cooperative – e.g. single dominant allele at first locus may influence expression of alleles at second locus•Complementary – e.g. 2 gene pairs may complement each other such that at least one dominant allele at each locus is required to express some phenotype•Novel phenotypes can happenEpistasis Overview•Production of organs (morphological/anatomical interactions)•Biochemical interactionsAnd here are the tricks to knowing it is epistasis (2 loci that affect each other):•ONLY a SINGLE CHARACTERISTIC is followed – assume genes not linked•Phenotypic ratios in 16th!!!Recessive Epistasis•Homozygous recessive masks expression at other locus•Two genes control fur color in mice•Agouti gene has 2 allelesA dominant agouti furaa homozygous recessive black•Albino gene has 2 allelesB dominant allows pigmentationbb prevents pigmentation regardless of A locus allelesGene B Gene ASuppose a true breeding albino mouse and a true breeding black mouse were interbred and all the F1 offspring were agouti. a)What are the genotypes of the P1 and F1 generation?b)What phenotypic ratio would you expect in the F2 generation if the F1 mice were interbred?c)What phenotypic ratio would you expect if the F1 mice were crossed with their albino parents?Individuals who have no H substance precursor (IOIO) cannot add either antigen (recessive mask – the homozygous presence of the mutant form of the FUT1 gene masks (epistatic) the expression of the IA and IB alleles, which are hypostatic)Recessive EpistasisBombay phenotype and the H factorDominant Epistasis•A dominant allele masks expression at other locus•Corn color•R gene controls aleurone color •R – dominant red•r recessive clear•C gene controls whether aleurone is pigmented•C’ dominant inhibitor of pigment - yellow•C allows pigment, dominant to c – red if R•c recessive inhibitor of pigment - yellowShow the resulting phenotypes of the following cross:RrC’c x RrCCComplementary Gene Interaction•Presence of dominant allele of each gene pair required to get a result•Sweet peas•White flowered sweet peas crossed – all F1 plants purple, F2 were 9/16 purple and 7/16 white•At least one dominant allele of each pair of 2 genes need to be present to get purpleComplementary Gene Interaction•Presence of dominant allele of each gene pair required to get a result•Sweet peas•White flowered sweet peas crossed – all F1 plants purple, F2 were 9/16 purple and 7/16 white•At least one dominant allele of each pair of 2 genes need to be present to get purple Precursor substance Gene A if A- intermediate product(colorless) (colorless) gene B if B- final product purpleAt least one dominant allele each gene necessary to assure both biochemical conversions to final purple productNovel Phenotypes•Biochemical pathways interact•Drosophila eyes at the brown and scarlet genes•Drosopterin – red pigment•Xanthommatin – brown pigment•With both, brick red•With neither, white•Cross 2 brick red flies get 9/16 brick: 3/16 brown: 3/16 scarlet: 1/16