BIOL 112 Lecture Notes - Lecture 17: Friedrich Miescher, Nucleic Acid Double Helix, Solvent
16 May 2018
School
Department
Course
Professor
Lecture'17'–'Non-Mendelian'Genetics'&'DNA'''''''''''(12/03/18)'
NON-MENDELIAN*GENETICS*
• Continuous*variation'='traits'don’t'fall'into'discrete'
categories,'they'fall'into'a'bell-curve.'Every'individual'
gene'still'follows'Mendel’s'laws.'
• Semi-dominant*trait'='get'a'mixture'of'phenotypes'
between'dominant'&'recessive'phenotype,'so'can'
distinguish'heterozygotes'&'homozygotes'
• Allelic*series'='Different'phenotypes'along'a'continuum.'''
o Can'still'only'have'2'alleles'in'an'individual,'but'the'population'as'a'whole'can'
have'individuals'that'have'many'different'alleles.'Everyone'doesn’t'have'to'have'
the'same'2.'
o E.g.'allelic'series'related'to'Alzheimer’s'disease'
§ ApoE'gene'determines'risk'of'getting'Alzheimer’s'
§ Have'e2,'e3,'e4'&'combo'of'these'alleles'determines'where'you'lay'in'the'
gradient'of'risk'
• Multigenic/Polygenic*trait*='more'than'one'gene'can'correspond'to'one'trait'(most'
often'the'case,'especially'in'human'health)'
o E.g.'heart'attack'risk'is'determined'by'genes'in'many'reasons'(on'chromosome'3,'
8,'14,'15,'etc.)''
§ Humans'have'different'amounts'of'alleles'that''
• In'broad'distribution,'you'cannot'distinguish'different'phenotypes'because'people'with'
the'same'genotype'might'not'necessarily'express'them'due'to'environmental'factors.'
• Environmental,contribution'to'phenotype'(true'of'most'phenotypes):'
o Penetrance:'percentage'of'individuals'of'a'given'genotype'that'show'the'
phenotype'at'all.'
§ E.g.'some'individuals'with'smooth,'wrinkled'pea'genotype'will'not'
express'the'phenotype.'
o Expressivity:'the'degree'to'which'a'phenotype'is'expressed'
§ E.g.'the'shades'of'a'flower.'
* *
2'
DISCOVERY*&*REPLICATION*OF*DNA*
• How,to,purify,something:,
o Separate'components'(usually'grind'the'cell,'or'chromatography)''
o Assay'each'component'(measure'the'component,'even'abstract'ones'like'
memory)'
• How,to,purify,DNA:'
o Grind'up'organism'
o Extract'lipids'&'proteins'with'organic'solvent'(e.g.'phenol)'
§ Friedrich'Miescher'isolated/discovered'nuclein'(DNA)''
o Precipitate'with'ethanol'
• How,to,purify,genetic,material:,
o Fredrick'Griffith'discovered'transforming+principle+(that'is'inherited'because'S'
bacteria'never'revert'back'after'receiving'hereditary'material'à'later'discovered'
to'be'DNA).*
§ Interested'in'making'a'vaccine'for'a'kind'of'pneumonia'caused'by'
bacteria.''
§ Then'he'performed'an'assay'to'discover'that'DNA'was'the'only'
component'able'to'convert'R'bacteria'into'S'bacteria.'
§ BUT,'DNA'wasn’t'completely'purified'so'people'were'worried'results'
were'due'to'contamination.'
3'
,
• Does,DNA,work,in,other,organisms?,
o Yes,'in'viruses'
§ Bacteriophages'are'viruses'that'infect'bacterial'
cells'by'“injecting”'genetic'material'into'bacterial'
cell.'
o The*Hershey-Chase*Experiment*
§ You'can'specifically'label'protein'with'
radioactive'sulfur'(DNA'never'has'sulfur)'
because'they'all'have'methionine'&'cytosine'
that'are'amino'acids'that'contain'sulfur.'
§ DNA'with'radioactive'phosphate'(proteins'
do'not'have'phosphorus)'
§ 1st'experiment:'
• Take'bacteriophage'with'labelled'
DNA'&'unlabeled'protein.'
• Infect'bacteria'&'genetic'material'is'
being'injected''
• In'blender,'protein'of'virus'will'be'
stripped'off'
• Radioactivity'will'be'in'pellet'with'the'
DNA'that'is'inside'the'bacteria.'
§ 2nd'experiment:'
• Radioactive'proteins'&'regular'DNA''
• Radioactivity'will'only'be'found'in'
supernatant.'
• Question:'What'if'Hershey'&'Chaxe'labeled'their'phage'
with'Carbon-14?'Which'fraction'would'be'radioactive?'
o Answer:'Both'the'supernatant'&'the'pellet'(because'carbon'is'found'in'DNA'&'in'
proteins)'
• What,properties,of,DNA,allow,it,to,be,the,genetic,material?,
o Chemical'structure'of'monomers'(A,'T,'G'&'C)'
o Chargraff’s*rules*
§ Discovered'that'bases'don’t'necessarily'exist'in'a'1:1:1:1'ratio'(more'A'&'
T'in'humans,'but'this'can'change'between'different'organisms)'
§ A'='T'&'G'='C'but'the'ratio'between'A+T/G+C'varies'between'organisms'
o Crystallography*
§ DNA'consists'of'2'strands'
§ Double'helix'
§ Phosphates'are'probably'on'the'outside'
§ Strands'run'antiparallel'
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BIOL 112 Full Course Notes
Verified Note
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Document Summary
Lecture 17 non-mendelian genetics & dna (12/03/18) Non-mendelian genetics: continuous variation = traits don"t fall into discrete categories, they fall into a bell-curve. Everyone doesn"t have to have the same 2: e. g. allelic series related to alzheimer"s disease. Apoe gene determines risk of getting alzheimer"s. Humans have different amounts of alleles that. E. g. some individuals with smooth, wrinkled pea genotype will not express the phenotype: expressivity: the degree to which a phenotype is expressed. Friedrich miescher isolated/discovered nuclein (dna: precipitate with ethanol, how to purify genetic material, fredrick griffith discovered transforming principle (that is inherited because s bacteria never revert back after receiving hereditary material later discovered to be dna). Interested in making a vaccine for a kind of pneumonia caused by bacteria. Then he performed an assay to discover that dna was the only component able to convert r bacteria into s bacteria. But, dna wasn"t completely purified so people were worried results were due to contamination.
