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LECTURE 11: FROM GENE TO PHENOTYPE II

LECTURE 11: FROM GENE TO PHENOTYPE II. chapter 6 questions & concepts genes & gene products allele interactions gene & protein interactions chi-square applications exam 1: problems. GENE & PROTEIN INTERACTIONS. how do you identify interacting genes?

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LECTURE 11: FROM GENE TO PHENOTYPE II

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  1. LECTURE 11: FROM GENE TO PHENOTYPE II • chapter 6 • questions & concepts • genes & gene products • allele interactions • gene & protein interactions • chi-square applications • exam 1: problems

  2. GENE & PROTEIN INTERACTIONS • how do you identify interacting genes? 1. generate new mutant alleles for a trait of interest by mutagenesis 2. test mutant alleles to determine if they represent alleles of multiple genes by (a) mapping & (b) complementation 3. combine mutant alleles to identify epistatic interactions

  3. GENE & PROTEIN INTERACTIONS • a complementation test will reveal allelic relationships 1 gene(below)... 1. dominance / recessiveness 2. semi-dominance = incomplete dominance 3. co-dominance (e.g.: IA & IB of ABO system) 4. multiple alleles (e.g.: IA, IB & i of ABO system) 5. conditional (e.g.: temperature sensitive) 6. lethality 7. sterility • ... or give wild type phenotypes 2 genes

  4. COMPLEMENTATION TEST • are mutations allelic (1 gene) or not (2 genes)? • test by making pair-wise crosses between mutants

  5. COMPLEMENTATION TEST

  6. COMPLEMENTATION TEST  gene  genes

  7. COMPLEMENTATION TEST • ... because the 2 mutations are in different genes

  8. GENE & PROTEIN INTERACTIONS • what is epistasis? text (1): a situation in which the differential phenotypic expression of a genotype at one locus depends on the genotype at another locus text (2): a mutation that exerts its expression while canceling the expression of the alleles of another gene Herr Doktor Professor: interactive expression of alleles at two (or more) genes (both of the text definitions are limiting)

  9. GENE & PROTEIN INTERACTIONS Mendelian phenotypic ratios

  10. GENE & PROTEIN INTERACTIONS • Mendelian dihybrid ratio

  11.  GENE & PROTEIN INTERACTIONS Mendelian dihybrid ratio parallel pathways dominant epistasis recessive epistasis duplicate additive genes duplicate dominant genes duplicate recessive genes recessive suppression (1) recessive suppression (2)

  12. PARALLEL PATHWAYS bw+/_; st+/_ 9 bw+/_; st/st 3 bw/bw; st+/_ 3 bw/bw; st/st 1 9 : 3 : 3 : 1

  13. PARALLEL PATHWAYS o+/_;b+/_9 o+/_; b/b 3 o/o; b+/_ 3 o/o; b/b 1 9 : 3 : 3 : 1

  14. DOMINANT EPISTASIS D/_; W/_ 9 d/d; W/_ 3 D/_; w/w 3 d/d; w/w 1 12 : 3 : 1 W  Dgene expression

  15. RECESSIVE EPISTASIS w+/_; m+/_ 9 w+/_; m/m 3 w/w; m+/_ 3 w/w; m/m 1 9 : 3 : 4

  16. DUPLICATE DOMINANT GENES A1/_; A2/_ 9 A1/_; a2/a23 a1/a1; A2/_ 3 a1/a1; a2/a21 15 : 1 1 dominant allele pigment

  17. DUPLICATE RECESSIVE GENES(aka COMPLEMENTARY GENE ACTION) C/_; P/_ 9 C/_; p/p 3 c/c; P/_ 3 c/c; p/p 1 9 : 7 1 recessive allele pigment

  18. REGULATING GENE & TARGET INTERACTION r+/_; a+/_ 9 r/r; a+/_ 3 r+/_; a/a 3 r/r; a/a 1 9 : 7

  19. (A POSSIBLE) SUPPRESSION MECHANISM

  20. su+ pd+ pd pd su+ su RECESSIVE SUPPRESSION pd+/_; su+/_ 9 pd+/_; su/su 3 pd/pd; su+/_ 3 pd/pd; su/su 1 13 : 3 mechanism for genotype  not explained by model

  21.  GENE & PROTEIN INTERACTIONS Mendelian dihybrid ratio parallel pathways dominant epistasis recessive epistasis duplicate additive genes duplicate dominant genes duplicate recessive genes recessive suppression (1) recessive suppression (2)

  22. MODIFIERS • modifier mutations influence expression of a mutation at a second locus • broadly used term (text gives a few examples) • gene activity can be modified by... • up- or down-regulation • enhancement or suppression

  23. SYNTHETIC LETHALS

  24. PENETRANCE & EXPRESSIVITY • penetrance: the % of individuals of given genotype that exhibit a phenotype... a population measurement • expressivity: the extent to which a given genotype is expressed at the phenotypic level... in each individual

  25. PENETRANCE & EXPRESSIVITY • can be due to... 1. environmental factors 2. genetic factors 3. unknown / difficult to measure (text) ??? • e.g., the rover / sitter foraging polymorphism

  26. GENE  GENE  PHENOTYPE GENE     BIOCHEMICAL PATHWAY:  PHENOTYPE   COMPETITION / INHIBITION:PHENOTYPE     ENZYME CATALYSIS:PHENOTYPE POLYGENY

  27. PHENOTYPE GENE PHENOTYPE PHENOTYPE    PLEIOTROPY SEQUENTIAL PHENOTYPES: GENE      RELATED PHENOTYPES: GENE      UNRELATED PHENOTYPES: GENE 

  28. GENE & PROTEIN INTERACTIONS        

  29. CHI-SQUARE APPLICATIONS red 77 orange 182 yellow 61 total 320 • example question on p. 209 • true-breeding P yellow x red petal plants  all orange petal F1. F1 are bred & F2 are... • with 3 phenotypes, reasonable hypotheses are... H1 = incomplete dominance... 1:2:1 ratio E = 80G1/G1 + 160G1/G2 + 80G2/G2 2 = 7.6, P < 0.025 (2.5%),  H1 

  30. CHI-SQUARE APPLICATIONS red 77 orange 182 yellow 61 total 320 • example question on p. 209 • true-breeding P yellow x red petal plants  all orange petal F1. F1 are bred & F2 are... • with 3 phenotypes, reasonable hypotheses are... H2 = recessive epistasis of ron Y & y... 9:3:4 ratio E = 180 Y/_; R/_ + 60 y/y; R/_ + 80 [Y/_; r/r + y/y; r/r] 2 = 0.15, P > 0.9 (90%),  H2 

  31. PRACTICE PROBLEMS you should be able to do CH6, p. 214 # 1 - 50

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