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LECTURE 10: FROM GENE TO PHENOTYPE I

LECTURE 10: FROM GENE TO PHENOTYPE I. exam 1: review chapter 6 questions & concepts genes & gene products allele interactions gene & protein interactions chi-square applications. CHAPTER 6: QUESTIONS. how do genes influence the organism? what are gene products?

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LECTURE 10: FROM GENE TO PHENOTYPE I

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  1. LECTURE 10: FROM GENE TO PHENOTYPE I • exam 1: review • chapter 6 • questions & concepts • genes & gene products • allele interactions • gene & protein interactions • chi-square applications

  2. CHAPTER 6: QUESTIONS • how do genes influence the organism? • what are gene products? • ... & what are they doing? • do alleles determine a specific phenotype? • how do genes interact? • can we dissect gene interactions using mutations?

  3. CHAPTER 6: CONCEPTS • if 2 haploid genomes (i.e., the gametes of diploids) each with 1 recessive mutation are combined mutant phenotype?... the mutations are allelic (they identify alleles of the same gene) or wild type phenotype?... the mutations are not allelic (they identify alleles of different genes)

  4. CHAPTER 6: CONCEPTS • dominance can be complete or incomplete • some mutations can cause lethality or sterility • expression of some mutations can be dependent on environment  conditional mutations • most traits are determined by sets of genes that interact with the environment • modified monohybrid ratios reveal allele interactions • modified dihybrid ratios reveal gene interactions

  5. GENE INTERACTION • genes never do anything by themselves • levels of interaction between alleles of 1. the same gene 2. different genes

  6. GENE INTERACTION • 3 ways to study these interactions 1. genetic analysis (ch 6) 2. functional genomics (ch 12) 3. proteomics (ch 12)

  7. GENES & GENE PRODUCTS • 1st clue from human “inborn metabolism error” • PKU (phenylketonuria) • autosomal recessive phenylalanine  tyrosine  phenylpyruvic acid (toxic)

  8. GENES & GENE PRODUCTS • “1 gene - 1 enzyme” hypothesis • Beadle & Tatum (1940s, Nobel Prize) • Neurospora crassa (haploid fungus) • mutants (by irradiation) & analysis

  9. supports growth of all genotypes GENES & GENE PRODUCTS

  10. GENES & GENE PRODUCTS

  11. GENES & GENE PRODUCTS

  12. GENES & GENE PRODUCTS • 3 arginine auxotrophs (arginine metabolism mutants) • mapped to different loci... different genes • growth on medium supplemented with different related compounds

  13. GENES & GENE PRODUCTS • chemical structure  biochemical pathway (B & T) enzyme X enzyme Y enzyme Z    precursor  ornithine  citrulline  arginine

  14. GENES & GENE PRODUCTS • results  arginine metabolism biochemical pathway arg-1+ arg-2+ arg-3+    enzyme X enzyme Y enzyme Z    precursor  ornithine  citrulline  arginine

  15. GENES & GENE PRODUCTS • results  “1 gene - 1 enzyme” hypothesis • more accurately “1 gene - 1 polypeptide” • most genes encode physical structure of proteins DNA mRNA polypeptide • some genes encode functional RNA only, e.g. • tRNA • rRNA

  16. GENES & GENE PRODUCTS

  17. GENES & GENE PRODUCTS

  18. ALLELE INTERACTION • interactions between alleles of one gene 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

  19. DOMINANT & RECESSIVE ALLELES • mutation recessive  + allele haplosufficient • mutation dominant  + allele haploinsufficient

  20. DOMINANT & RECESSIVE ALLELES • dominant & recessive alleles... P F1 F2 red x white  redxred  ¾ red + ¼ white 3 : 1

  21. INCOMPLETELY DOMINANT ALLELES • incomplete dominance (= semidominance)... P F1 F2 red x white  pinkxpink  ¼ red + ½ pink + ¼ white 1 : 2 : 1 • phenotypes are quantitatively different

  22. INCOMPLETELY DOMINANT ALLELES • are pink flowers more red or more white? • why is this not blending?

  23. CODOMINANT ALLELES • ABO blood type • i recessive to both dominant alleles (IA & IB > i) • IAIB is AB, qualitatively different from A or B

  24. MULTIPLE ALLELES • ABO blood type • 6 possible genotypes & 4 possible phenotypes • influences variation of trait in populations

  25. CONDITIONAL ALLELES • influenced by environment, e.g.: • temperature (hot or cold) • desiccation • nutrient requirement • chemicals • infection

  26. CONDITIONAL ALLELES • e.g.: temperature sensitive shibire (paralyzed) mutant P F1 F2 shi+ x shits  shi+/shits x shi+/shits  all active @ 25º 1 • shitswild type @  25º = permissive temperature

  27. CONDITIONAL ALLELES • e.g.: temperature sensitive shibire (paralyzed) mutant P F1 F2 shi+ x shits  shi+/shits x shi+/shits  ¾ active + ¼ paralyzed @ 29º 3 : 1 • shitsparalyzed @  29º = restrictive temperature

  28. LETHAL ALLELES • homozygotes lethal (can be dominant or recessive) • e.g., yellow (AY) allele in mice

  29. don’t see these LETHAL ALLELES • homozygotes lethal (can be dominant or recessive) • e.g., yellow (AY) dominant allele in mice AY/A  x AY/A   ¼ AY/AYlethal + ½ AY/A yellow + ¼ A/A black P F1 • 2/3 AY/A yellow + 1/3 A/A black

  30. 2/3 curly + 1/3 wild type LETHAL ALLELES • e.g.: Curly (Cy) mutations in Drosophila P F1 Cy– Cy– Cy+ Cy+  ¾ alive + ¼ dead 3 : 1 —— x ——

  31. STERILE ALLELES • homozygotes sterile (can be dominant or recessive) • e.g., fruitless (fru) allele in Drosophila

  32. STERILE ALLELES • homozygotes sterile (can be dominant or recessive) • e.g., fruitless (fru) allele in Drosophila fru+/fru  x fru+/fru   ¾ wild type + ¼ fruitless fru/fru fruitless  x fru+/fru+wild type    do not mate, no progeny P F1 F2

  33. mbmB+ mbmB– • homozygous mbmB–live but give no offspring STERILE ALLELES • e.g.: mushroom body miniature B (mbmB) mutations P F1 mbmB– mbmB– mbmB+ mbmB+  ¾ alive + ¼ sterile 3 : 1 ———— x ————

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