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Lecture 2 (continue) Modifications to Mendelian Genetics Complexities in relating phenotypes to genotypes

Lecture 2 (continue) Modifications to Mendelian Genetics Complexities in relating phenotypes to genotypes. Dominant epistasis. The dominant allele of the first gene block the expression of the second gene regardless of the second gene’s alleles. white AABB x aabb green. F1 AaBb (white).

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Lecture 2 (continue) Modifications to Mendelian Genetics Complexities in relating phenotypes to genotypes

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  1. Lecture 2 (continue) Modifications to Mendelian Genetics Complexities in relating phenotypes to genotypes

  2. Dominant epistasis The dominant allele of the first gene block the expression of the second gene regardless of the second gene’s alleles. white AABB x aabb green F1 AaBb (white) F2 12 (white): 3 (yellow): 1 (green) 9/16 A_B_ white 3/16 aaB_ white 3/16 A_bb yellow 1/16 aabb green b(enzyme) A(enzyme) Precusor (white) -----> green pig. -------> yellow pig.

  3. Dominant epistasis • fruit color of summer squash Difference btw this and monhybrid F1 looks same with dom/reccesive F2 is neither 3:1 or 1:2:1 ratio and also additional new phenotype (yellow)

  4. Testcross of F1 with dominant epistasis Not the expected 1:1 ratio! AaBb x aabb [white x green] 1/4 AaBb ------- A_B_ ( ) 1/4 Aabb -------- A_bb ( ) 1/4 aaBb -------- aaB_ ( ) 1/4 aabb -------- aabb ( ) b(enzyme) A(enzyme) Precusor (white) -----> green pig. -------> yellow pig.

  5. Testing genetic models with chi-square test Consider the following genetic data collected from the crossing of snapdragons. Flower colors of snapdragons can be red, pink or white; leaf color can be green or yellow. You get the following numbers of offspring by crossing two pink-flowered, yellow-leaved snapdragons. What genetic models can be applied to explaining the inheritance patterns of flower and leaf colors? Phenotypes obs. No. Red flowers, green leaves 10 Pink flowers, green leaves 19 White flowers, green leaves 9 Red flowers, yellow leaves 17 Pink flowers, yellow leaves 28 White flowers, yellow leaves 13 Total 96 Think each trait Flower color self-cross of one phenotype results in three categories of phe. Candidate model Incomplete dominance (1:2:1) vs Recessive epistasis (9:3:4)

  6. Testing genetic models with chi-square test Consider the following genetic data collected from the crossing of snapdragons. Flower colors of snapdragons can be red, pink or white; leaf color can be green or yellow. You get the following numbers of offspring by crossing two pink-flowered, yellow-leaved snapdragons. What genetic models can be applied to explaining the inheritance patterns of flower and leaf colors? Phenotypes obs. No. Red flowers, green leaves 10 Pink flowers, green leaves 19 White flowers, green leaves 9 Red flowers, yellow leaves 17 Pink flowers, yellow leaves 28 White flowers, yellow leaves 13 Total 96 Think each trait 2) Leaf color Self-cross of one phenotype results in two categories of phe. Candidate models Complete dominance (3:1) vs Lethal allele (2:1) vs Complementation (9:7)

  7. Testing genetic models with chi-square test 1) Model 1 (flower incomplete dom; leaf color complete dom) Phenotypes obs. No. exp ratio (exp No) (O-E)2/E Red flowers [1/4], green leaves [1/4] 10 1/4 x 1/4= 1/16 ( ) Pink flowers [2/4], green leaves [1/4] 19 2/4 x 1/4= 2/16 ( ) White flowers [1/4], green leaves [1/4] 9 1/4 x 1/4= 1/16 ( ) Red flowers [1/4], yellow leaves [3/4] 17 1/4 x 3/4= 3/16 ( ) Pink flowers [2/4], yellow leaves [3/4] 28 2/4 x 3/4= 6/16 ( ) White flowers [1/4], yellow leaves [3/4] 13 1/4 x 3/4= 3/16 ( ) Total 96 16/16 =1 (96) df = ? ; 2 = ?

  8. Testing genetic models with chi-square test 2) Model 2 (flower incomplete dom; leaf color lethal allele) Phenotypes obs. No. exp ratio (exp No) (O-E)2/E Red flowers [1/4], green leaves [1/3] 10 1/4 x 1/3= 1/12 ( ) Pink flowers [2/4], green leaves [1/3] 19 2/4 x 1/3= 2/12 ( ) White flowers [1/4], green leaves [1/3] 9 1/4 x 1/3= 1/12 ( ) Red flowers [1/4], yellow leaves [2/3] 17 1/4 x 2/3= 2/12 ( ) Pink flowers [2/4], yellow leaves [2/3] 28 2/4 x 2/3= 4/12 ( ) White flowers [1/4], yellow leaves [2/3] 13 1/4 x 2/3= 2/12 ( ) Total 96 16/16 =1 (96) df = ? ; 2 = ?

  9. Testing genetic models with chi-square test Model 1: df = ? ; 2 = ? Which one is right? Model 2: df = ? ; 2 = ?

  10. Summary of Gene Interactions I

  11. Summary of Gene Interactions II

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