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  Test for Linkage

  Test for Linkage. (P). AA BB. aa bb. LOCUS 2. B b. Total. Obs: 140 Exp: 255(250/500) = 127.5. Obs: 110 Exp: 245(250/500) = 122.5. 2 5 0. A a B b. aa bb. L O C U S 1. A a. Progreny Counts. Obs: 115 Exp: 255(250/500)

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  Test for Linkage

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  1. Test for Linkage (P) AA BB aa bb LOCUS 2 B b Total Obs: 140 Exp: 255(250/500) = 127.5 Obs: 110 Exp: 245(250/500) = 122.5 2 5 0 Aa Bb aa bb L O C U S 1 A a Progreny Counts Obs: 115 Exp: 255(250/500) = 127.5 Obs: 135 Exp: 245(250/500) = 122.5 2 5 0 AaBb Aabb aaBb aa bb 140 110 115 135 Total 2 5 5 2 4 5 5 0 0 H0: The loci are NOT linked. calc > crit H0 can be rejected. The loci do not assort independently. calc = 5.002 df = (dfrows) x (dfcolumns) = 1 crit = 3.841

  2. Molecular Basis for Relationship between Genotype and Phenotype genotype DNA DNA sequence transcription RNA translation amino acid sequence protein function phenotype organism

  3. One Gene/One Enzyme Hypothesis (Beadle and Tatum) Wild-type Neurosporacrassa (red bread mold) is prototrophic. Prototrophs are able to grow on minimal medium. Minimal medium contains only inorganic salts, simple carbon source, and water. Auxotrophs require nutritional supplement(s) for growth.

  4. One Gene/One Enzyme Hypothesis (Beadle and Tatum) Conidia are mutagenized with X-ray. Possible mutants are crossed to wild-type and individual ascospores are cultured on complete (permissive) medium. Cultures are plated on minimal medium and auxotrophs are isolated. Auxotrophs are tested for nutritional requirement.

  5. One Gene/One Enzyme Hypothesis (Beadle and Tatum) Each requirement for a specific nutrient (mutant effect) followed Mendelian pattern of inheritance. Beadle and Tatum deduced that each mutant was deficient for an essential enzyme in a biosynthetic pathway. A_ B_ enzyme A enzyme B compound Y compound X compound Z A_ bb enzyme A compound Y compound X

  6. Not All Gene Products are Enzymes! One Gene/One Enzyme One Gene/One Polypeptide (structural proteins, subunits) One Gene/One Product (rRNA, tRNA)

  7. Mutants of Arginine Biosynthetic Pathway cit GSA arg orn glu + + 0 0 0 Mutant 1 + + + + 0 Mutant 2 + + + 0 0 Mutant 3 + 0 0 0 0 Mutant 4 cit citrulline GSA glutamic semi-aldehyde arg arginine orn ornithine glu glutamic acid

  8. Mutants of Arginine Biosynthetic Pathway Order of Compounds in Pathway Determination of Mutant Effects cit citrulline GSA glutamic semi-aldehyde arg arginine orn ornithine glu glutamic acid

  9. Molecular Basis for Relationship between Genotype and Phenotype genotype DNA DNA sequence transcription RNA translation amino acid sequence protein function phenotype organism

  10. Gene Sites Sensitive to Mutation null if splice junction is affected no effect if mutation is in the middle of the intron or not the branch point

  11. Complementation Analysis AllelicNon-Allelic m1 m2 m1 m2 Cis Trans + + + + Wild-type Wild-type + m2 + m2 m1 + m1 + Mutant Wild-type Mutant alleles complement if wild-type phenotype results when two haploid genomes carrying different mutations are united in the same cell.

  12. How many loci are represented here? Mutant I X Mutant II F1 a b c d e f o + + o o + a + o + + + + b + + o + + o c o + + o o + d o + + o o + e + + o + + o f

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