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Rules: Cell phones off Computers only for class related work No food or drink in lab room

Biol 423L Laboratories in Genetics. Rules: Cell phones off Computers only for class related work No food or drink in lab room Text Book: Hartwell et al., 2nd Edition 2004 Genetics from Genes to Genomes Mc Graw-Hill, Boston. Web page: www.bio.unc.edu/courses/2006Fall/Biol423L.

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Rules: Cell phones off Computers only for class related work No food or drink in lab room

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  1. Biol 423L Laboratories in Genetics Rules: Cell phones off Computers only for class related work No food or drink in lab room Text Book: Hartwell et al., 2nd Edition 2004 Genetics from Genes to Genomes Mc Graw-Hill, Boston. Web page: www.bio.unc.edu/courses/2006Fall/Biol423L

  2. Goals for course: Reinforce basic genetic principles Introduce model organisms commonly used by geneticists Learn how genetics is used to understand Disease Biochemical pathways Development

  3. Lab reports: Abstract Introduction Results Discussion Course information page has instructions about preparing your lab reports.

  4. Grading: Lab Reports: 50% of grade 5% of that is participation 1 day late, 50% off more than that will only be graded under special circumstances. Research Paper: 10% of grade Topics due Oct. 9. Outline due Oct. 23. Paper due Nov. 29 2 quizzes: 10% each of final grade. Oct. 2 and Nov. 13. Final exam: 20% of final grade comprehensive Dec. 11.

  5. Genes Alleles and Epistasis

  6. Genetics starts with observation Observe variability Use genetics to understand the cause of the variability. What proteins or RNAs are responsible for the variability you can see?

  7. Easy example, flower color

  8. How many genes affect flower color? How variable are the proteins encoded by those genes? What is the pathway to make flower color?

  9. List of terms: Trait: some aspect of an organism that can be observed, measured Phenotype: the way a trait appears in an individual, the combination of genotype and environment. Genotype: the constitution of alleles at any gene in an individual. Gene: continuous stretch of DNA sufficient to encode a messenger RNA or a functional RNA. Locus: A region of a chromosome, usually for a single gene. Messenger RNA: the RNA message for a single protein. Allele: a variant of the sequence of a given gene. Diploid: an individual with two copies of each chromosome. Haploid: an individual with one copy of each chromosome.

  10. How many genes affect flower color? How variable are the proteins encoded by those genes? What is the pathway to make flower color?

  11. First make sure the types are heritable and true breeding (homozygous for flower color alleles) All uniform purple by purple (self) X Homozygous: a diploid individual with two copies of the same allele for a given gene. Heterozygous: a diploid individual with two different alleles for a given gene.

  12. What are the relationships between color types? X Purple is dominant to Red

  13. What are the relationships between color types? X Purple is dominant to white

  14. 1. How many genes are required to make purple pigment in flowers? Complementation tests can be made between recessive alleles. A dominant allele cannot be used. Why?

  15. Allelism test: Cross different white flowered plants If the mutations are in the same gene, The progeny will be white X White 1 White 1

  16. Allelism test: Cross different white flowered plants If the mutations are in different genes, The progeny will be pigmented X White 1 White 2

  17. Allelism or complementation test If plants with recessive alleles are crossed and the progeny also have the recessive trait, The alleles are variants of the same gene If plants with recessive alleles are crossed and the progeny have the dominant trait, The alleles are variants of different genes

  18. Pathway to purple Precursor 1 White1 Intermediate White2 Purple

  19. White 2 Purple X White 1 RrAa rrAA RRaa

  20. Using multiple allelism tests with diverse recessive mutants, We can identify all the genes specifically involved in making the purple pigment

  21. Genetics can be used to determine the Order of steps in a biological pathway Epistasis tells which gene products act earlier or later in a process.

  22. What are the relationships between color types? X Purple is dominant to White 1

  23. Purple is dominant to White1 White1 rr Purple RR X Purple Rr F1 X F2 1 RR, 2Rr and 1rr

  24. Punnet square Female gametes Male gametes r R R RR Rr r rr Rr

  25. What are the relationships between color types? X pp PP Pp Purple is dominant to Red

  26. Epistasis Two genes for flower color Two steps in a pathway to make pigment Where are the two genes in the pathway?

  27. Purple is either a mixture of blue and red pigments or Purple results from modification of the same precursor from a white precursor to a red intermediate and finally a purple pigment. We can use genetics to distinguish the two possibilities. The effect of variant alleles in multiple genes that affect pigment in combination will answer the question.

  28. Pathway 2 Pathway 1 Precursor 1 Precursor 2 Precursor 1 R R P Red Red Blue P Coexpression of Blue and red pigment derived from different precursors Makes purple Purple Modification of the same precursor leads to first a red pigment and then a purple pigment

  29. Relationship between White1 and Red X White1 rrPP Red RRpp X F1 is all Purple RrPp F2 3 4 9

  30. Punnet Square: two genes with randomly segregating alleles RrPp X RrPp Female gametes Male gametes rp RP Rp rP RP RRPP RRPp RrPP RrPp RRPp RrPp Rrpp RRpp Rp rP RrPP RrPp rrPP rrPp rp RrPp Rrpp rrPp rrpp 9R_P_ 3R_pp 3rrP_ 1rrpp

  31. 9R_P_ 3R_pp 3rrP_ 1rrpp Phenotypes: Purple White Red White White - no pigment Precursor 1 No R - get no red precursor Neither purple nor red pigment can be made R Red P No P – get red pigment but not purple Purple

  32. If Pathway 1 Precursor 2 Precursor 1 R P Red Blue Coexpression of Blue and red pigment derived from different precursors Makes purple

  33. 9R_P_ 3R_pp 3rrP_ 1rrpp Phenotypes: Purple White Red Blue R no P would make red pigment only No R but P would make blue pigment, Fact that loss of R changes phenotype to rr even if Functional P is expressed indicates that P and R affect a common pathway and R is before P in the pathway to make pigment.

  34. Yeast complementation test for next week: Brewers Yeast Saccharomyces cerevisiae: 16 chromosomes 12,052 kb DNA 6183 ORFs About 5800 expected to encode proteins

  35. Yeast is a very useful model for genetics because of its life cycle Haploid life cycle

  36. Yeast is a very useful model for genetics because of its life cycle Mating cycle Diploid

  37. We can isolate mutants as haploids We can test the mutations for allelism by a complementation test Two haploids are mated. The resulting Diploid has both mutations. Either the mutations are allelic and do not complement, or they are mutations in two different genes and they do complement.

  38. a2 a1 a1 Select mutants that are defective in Adenine synthesis- cannot grow without adenine in medium. Turn red on media with adenine because an adenine precursor accumulates.

  39. X a1 a1 a1 a2 a2 X a1 a1 Which mating results in complementation?

  40. Lab experiment: Corn kernels R and P RR or Rr is full color rr is no color PP or Pp are full color pp is weak color Question is pprr weak color? P epistatic to R or Is pprr no color? R epistatic to P

  41. End

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