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White CCpp P Cp Purple CcPp F1 X White ccPP X Cp Purple CcPp F2 CP Cp cP CP CCPP Purple CCPp Purple CcPP Purple CcPp Purple Cp CCPp Purple CCpp White CcPp Purple Ccpp White cP CcPP Purple CcPp Purple ccPP White ccPp White cp CcPp Purple Ccpp White ccPp White ccpp White Summary: 9/16 purple, 7/16 white cp AABB X aabb ab AB AaBb AB P X Ab Gametes AaBb aB F1 x F1 ab AB White White White White Ab White White White White aB White White Yellow Yellow ab White White Yellow Green Where A--- is white, aaB- is yellow, and aabb is green. aabb aaBB aaBb AAbb Aabb AABB AABb AaBB AaBb Genotypes Interactions _______________________________________________________________________________________ Epistasis Dominance Phenotypic Classes Example Phenotypes _______________________________________________________________________________________ (Classical Complete ratio) for A,B 9 3 3 1 Garden peas seed color and surface texture 9 yellow round 3 yellow wrinkled 3 green round 1 green wrinkled None Complete X-X- 3 0? 1 Guinea pig 3 short yellow for A, incomplete for B -X- hair length and color (X) 6 short cream (-) 3 short white 1 long yellow (0) 2 long cream (? ) 1 long white ? 66 aabb aaBB aaBb AAbb Aabb AABB AABb AaBB AaBb _______________________________________________________________________________________ Epistasis Dominance Phenotypic Classes Example Phenotypes _______________________________________________________________________________________ aa epistatic Complete 9 3 4 Mice coat pattern 9 agouti to B,b for A,B and color or 3 colored (Recessive) Labrador 4 white retriever color A epistatic to B,b (Dominant) Complete for A,B 12 3 1 Summer squash fruit color or Foxglove color 12 white 3 yellow 1 green A epistatic to B,b; bb epistatic to A,a (Dominant and Recessive) Complete for A,B 13 3 1 Chicken color 13 white 3 colored aa epistatic to B,b; bb epistatic to A,a (Duplicate Recessive) Complete for A,B 9 Daisy color or white and purple flower color 9 purple 7 yellow center A epistatic to B,b; B epistatic to A,a (Duplicate Dominant) Complete for A,B 15 Shepherd's purse seed capsules 15 triangular 1 ovoid 7 1 66 cont. Epistatic gene interaction: 1) One distinct phenotype in each phenotypic classrather than two, although two separate genes are being considered. 2) “Novel” or new phenotypes may appear in the F1 and/or F2 generations that had not appeared in the P generation. 3) Phenotypic ratio in F2 is altered from classical ratio (ex. 9:3:4, 12:3:1, 13:3, 9:7, 15:1) 4) “Masking” effect. Masking (non-allelic) is not the same as dominance (allelic). Five forms of epistasis and their corresponding F2 phenotypic ratios: • 1) Recessive (9:3:4), aa epistatic to B,b. • 2) Dominant (12:3:1), A epistatic to B,b. • 3) Dominant and Recessive (13:3), A epistatic to B,b, and/or bb epistatic to A,a. • 4) Duplicate Recessive (9:7), aa epistatic to B,b, and/or bb epistatic to A,a. • 5) Duplicate Dominant (15:1), A epistatic to B,b, and/or B epistatic to A,a. 9 A _B_ : 3 A_bb : 3 aaB_ : 1 aabb • 1) 9 A _B_ : 3 A_bb : 4 aaB_ , aabb • 2) 12 A _B_ , A_bb : 3 aaB_ : 1 aabb • 3) 13 A _B_ , A_bb , aabb: 3 aaB_ • 4) 9 A _B_ : 7 A_bb , aaB_ , aabb • 5) 15 A _B_ , A_bb , aaB_ : 1 aabb Epistatic Metabolic models: Step - Type 1) Recessive Allele A Allele B Enzyme A White (Precursor) Enzyme B Colored (Intermediate) Agouti (Final Product) 2) Duplicate Recessive Allele A Allele B Enzyme A Enzyme B Yellow (Precursor) Yellow (Intermediate) Purple (Final Product) Simultaneous 1) Duplicate Dominant Allele A Enzyme A Triangular (Final Product) Ovoid (Precursor) Enzyme B Allele B Metabolic pathway models at which 3 of the 5 forms operate: • 1) Step-type: • Recessive (9:3:4)-2 conversions and 3 metabolites (phenotypes)-precursor, intermediate, and final product are different. • Duplicate Recessive (9:7)-2 conversions and 3 metabolites (phenotypes)-precursor and intermediate are the same, but final product different. • 2) Simultaneous: • Duplicate Dominant (15:1)-1 conversion and 2 metabolites (phenotypes)-precursor and final product are different, with no intermediate. Illustrate recessive epistasis by filling in all blanks below. Circle all gametes. aa epistatic to B,b. A_B_ = agouti mouse, A_bb = colored mouse; aaB_, aabb = white mouse. P Phenotypes Genotypes Gametes F1 Phenotypes Genotypes Gametes F2 Genotypes F2 Phenotypes F2 Phenotypic ratio F2 Genotypic ratio x x x x x x AAbb . aaBB .. .. .. .. . . . . . ..: ..: USE THE INFORMATION ABOVE TO MAKE A TESTCROSS BELOW F1 Parent Testcross Parent Phenotypes x Genotypes x Gametes x Testcross Progeny Phenotypes Genotypes . . . . . . Testcross Phenotypic Ratio Testcross Genotypic Ratio . . Illustrate recessive epistasis by filling in all blanks below. Circle all gametes. aa epistatic to B,b. A_B_ = agouti mouse, A_bb = colored mouse; aaB_, aabb = white mouse. P F1 Phenotypes colored x white Genotypes AAbb x aaBB Gametes 1/1 Ab x 1/1 aB Phenotypes agouti x agouti Genotypes AaBb x AaBb Gametes 1/4 AB 1/4 Ab 1/4 aB 1/4 ab x 1/4 AB 1/4 Ab 1/4 aB 1/4 ab F2 Genotypes F2 Phenotypes F2 Phenotypic ratio F2 Genotypic ratio . . . . Working space Working space 9:3:4 4:2:2:2:2:1:1:1:1 . . .: .: . USE THE INFORMATION ABOVE TO MAKE A TESTCROSS BELOW F1 Parent Testcross Parent Phenotypes agouti x Genotypes AaBb x Gametes 1/4 AB 1/4 Ab 1/4 aB 1/4 ab x white aabb 1/1 ab Testcross Progeny Phenotypes agouti colored . Genotypes white white Testcross Phenotypic Ratio Testcross Genotypic Ratio 1/4 AaBb 1/4 Aabb 2:1:1 1:1:1:1 63 1/4aaBb 1/4 aabb . . . . . Example of recessive epistasis (Labrador retriever coat color): A = allows for deposition of either black or brown color in coat; aa = prevents deposition of color (black or brown) pigment in coat (epistatic gene pair); B = black; b = brown. Photo (a) A B Photo (c) *aaB A bb Photo (b) *This dog has a black nose and black lips and would, therefore, be aaB_ (lacks black pigment in hair, but not in skin). If it was aabb it would have yellow hair and light colored skin [see nose and lips of dog in photo (b)].