Welcome to Genetics (BIOL 364/564)
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Welcome to Genetics (BIOL 364/564)
Dr. Carol Ely Hepfer
Textbook and Study Guide:
iGenetics: A Molecular Approach, third edition
Author: Peter J. Russel
Publisher: Pearson/Benjamin Cummings
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Materials Available at Desire 2 Learn (D2L)
In ‘Content’ Area
Syllabus, Handouts, PowerPoint slides, Pencasts
Discussions - Group Lockers, Drop Boxes
Announcements - Marauder email essential
PLEASE - LOG OUT!!!
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Handouts
Syllabus
Lecture Slides (available at D2L, not comprehensive)
Lab Handouts
*Alternative Transformation Protocol*
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What is Genetics?
Biological Study of Inheritance
Inherited traits are determined by genes that are transmitted from parents to offspring during sexual reproduction.
Chi-Chon
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Areas of Study within Genetics
Population Genetics, Quantitative Genetics
Molecular Biology
Cytogenetics
TransmissionGenetics
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History of Genetics
~~ Agriculture, Breeding
1859 Charles Darwin - ‘Origin of the Species’, evolution, natural selection
1866 Gregor Mendel - Research published on inheritance in peas
1869 Friedrich Miescher - Discovered nucleic acids
1900 Hugo deVries, Carl Correns, Erich vonTschermak -Rediscovered Mendel
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History of Genetics
1908 Archibald Garrod - ‘Inborn Errors of Metabolism’,
defective enzymes cause human diseases
1928 Frederick Griffith - Phenotype transformation observed in bacteria
1944 Oswald Avery, Colin MacLeod, MacLyn McCarty - DNA is the genetic material in bacteria
1952 Alfred Hershey, Martha Chase - DNA is the genetic material in some viruses
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History of Genetics
1950s Rosalind Franklin, Maurice Wilkins - Xray crystallography of DNA
1953 James Watson, Francis Crick - Deduced three dimensional structure of DNA
1970s Numerous investigators - Deciphered the genetic code Molecular Biology begins
1990s Human genome project initiated - Genomics, Proteomics, etc.,
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Gene expression determines phenotype
Phenotype - outward appearance of an individual
ExamplesPlant Height - Tall, Dwarf Hair Texture - Curly, Wavy StraightYeast Metabolism - Produces ASN, Requires ASNBacterial Resistance - Tetracycline, Ampicillin
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Classification of Phenotypes
Wild type (+) = most common phenotype in population, ‘normal’
Mutant = unusual, variant form, due to changes (mutations) in gene(s)
Examples:Trait Wild type MutantEye color Red White, scarlet, brownColoration Pigmented Albino
Whippets
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What is a gene?
Mendelian
Cytogenetic
Molecular
Abstract unit of inheritance - A a B b
Location along a chromosome gene locus
Sequences of bases in DNA
5’ ATCGCTGTCAGTCCTAGA 3’ OR
5’ ATCGCTCTCAGTCCTAGA 3’
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Discovery that DNA is the genetic material
Genes - control phenotype, located on chromosomes
Chromosomes - composed of DNA, RNA, protein
1940’s -
Proteins favored as candidate - sufficiently complex
Nucleic acids - too simple
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Preliminary Evidence in favor of DNA
1. Genes and chromosomes - in nucleus, not cytoplasm Proteins and RNA - in nucleus and cytoplasm DNA - mostly in
nucleus
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Preliminary Evidence in favor of DNA
2. [DNA] # of chromatids
G1 cells - 1 X [DNA] (unreplicated chromosomes)
G2 cells -2X [DNA]
(replicated chromosomes)
[DNA] in diploid cells = 2x that in haploid cells
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Preliminary Evidence in favor of DNA
3. Chemical composition of DNAConsistent within each speciesSame in all cells of an individual
RNA and Proteins differ substantially in different cells of the same
individual
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Preliminary Evidence in favor of DNA
4. UV light (260 nm)
Wavelength of maximum absorbance for DNA
Highly mutagenic
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Griffith’s Transformation Experiment (1928)
Diplococcus pneumoniae
Antigen type (II or III)
Colony shape Smooth (S) - encapsulated, virulent
Rough (R ) - no capsule, avirulent
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Griffith’s Transformation Experiment
What is going on?
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Interpreting Griffith’s Transformation Experiment
Could mutations in IIR cells transform them into IIIS?
Something from dead IIIS cells ‘transforms’ IIR into IIIS
Probability of one mutation~ 1 in 1,000,000
Probability of two mutations< 1 in 1012
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What is Griffith’s Transforming Principle?
Avery, MacLeod, McCarty (1944)
Extract from virulent (S) bacteria isolated
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Avery, Macleod, McCarty Experiment
Extract from III S
protease
Is it DNA or RNA?
RNase
DNase
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Hershey & Chase Experiment
Experimental organism - T2 bacteriophage - composed of protein and DNA
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Hershey & Chase Experiment
Life cycle of T2 bacteriophage
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Hershey & Chase Experiment
Phage inject genetic information into bacteria Is it their DNA or their protein?
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Hershey & Chase ExperimentAllow infection, separate bacteria from phage
Centrifuge
Centrifuge
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Identity of Genetic Material Established
Most organisms - DNA
Some viruses - RNA
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Chemical Composition and Structure
DNA and RNA - polymers of nucleotides
Each nucleotide - sugar, base, phosphate
Different functional group at carbon #2
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Chemical Composition and Structure
Nitrogenous Bases
Purines
Pyrimidines
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Chemical Composition and Structure
DNANucleosides:deoxyadenosinedeoxyguanosinedeoxycytidinedeoxythymidine
Nucleotides:-monophosphate
dAMP, etc.
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Chemical Composition and Structure
RNANucleotides
adenosinemonophosphate,
uridinemonophosphate,
etc.
AMP, UMP, etc.
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Chemical Composition and Structure
DNA and RNA polymers ofnucleotides
3’-5’ phosphodiesterlinkage
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RNA is normally single-stranded
Secondary structures - intrastrand H-bonding
Ex. Stem and Loop
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Evidence that DNA is double-stranded
Chemical composition
Chargaff (1947)[C] =
[G][A] = [T]
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Evidence that DNA is helical
Physical chemistry - Franklin & Wilkins (1952)
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Evidence that DNA is helical
O
Xray diffraction
helical structure20 A diameterhighly orderedrepeating units
3.4 A
34 A
Note: 1 A = 0.1 nm
O
O
O
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Watson and Crick
Model building to deduce structure (1953)
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Watson and Crick Model for DNA
DNA Bright-handed
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Specific Base Pairing in DNA
Hydrogen Bonding
A with T
C with G
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Arrangement of DNA strands
Antiparallel
Complementary
5’ TGTA 3’3’ ACAT 5’
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Different Forms of DNA
A-DNA B-DNA Z-DNA
right-handedtight coiling
left-handedloose coiling
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Organization of Chromosomes - Viruses
dsDNA, ssDNA, dsRNA, ssRNAcircular, linearsingle chromosome, segmented genome
T-even phages (T2, T4, T6) - dsDNA, 1 linear chromosomeX174 - ssDNA, one circular chromosomeLambda () - dsDNA, alternates linear and circular
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Organization of Chromosomes - Prokaryotes
Most - single circle, dsDNASome - linearExtra chromosomes, Plasmids
Cells Divide by Binary Fission
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Organization of Chromosomes - Prokaryotes
A. tumefaciens - 1 circular + 1 linear chromosome (3.0 Mb) (2.1 Mb)
E. coli - 1 circular chromosome + circular plasmids (4.6 Mb)
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Organization of Chromosomes - ProkaryotesDNA supercoiled into nucleoid region of cell
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Organization of Chromosomes - Eukaryotes
Replicated metaphase chromosome
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Organization of Chromosomes - Eukaryotes
DNA supercoiled to fit into chromosomes
Relaxed DNA in haploid (1n) human cell = 1 meter long
DNA in largest chromosome = 82 mm longMetaphase chromosome = 10 m long
Analogy: 25 miles of rope coiled into 2 ft x 16 ft canoe
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Organization of Chromosomes - Eukaryotes
Chromatin - DNA supercoiled with proteins
Histones - small, basic (+), bind DNA (-)H1, H2A, H2B, H3, H4
Nonhistones - all other associated proteins- many acidic (+), bind histones- include those for repair, replication, etc.
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Nucleosome Structure
DNA (147 bp) wrapped around histone octamer
10 nm chromatin fiber - string of nucleosomes
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Chromatin Structure
10 nm chromatin fiber - condensed with H1
30 nm chromatin fiber - solenoid model
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Chromatin in Metaphase Chromosome
Metaphase chromosome with histones removedNonhistone scaffold
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Euchromatin and Heterochromatin
Euchromatin - staining intensity varies with cell cycle as chromatin condenses and
relaxes actively transcribed no repetitive sequences
Heterochromatin - remains condensed (darkly staining)often replicates latertranscriptionally inactive
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Types of Heterochromatin
Constitutive - present in all cells at same location usually repetitive DNA
Ex. centromere region
Facultative - varies with cell type, stage, locationEx. inactive X chromosome
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Centromeric DNA
Repetitive sequences, Constriction where sister chromatids are joined,Important for chromosome segregationVary in size and sequenceBind proteins, site of kinetochore formation
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Telomeric DNA
Ends of chromosomes, tandem repeatsStability and replication of chromosome ends
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Unique Sequence DNA
One copy per haploid cellMost protein encoding genesOther sequences also unique ~ 55-60 % of human genome
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Repetitive Sequence DNA
Numerous copies in genome
Dispersed Repeats (INterspersed Elements)
LINEs - 1,000 to > 7,000 bp
LINE1 (~500,000 copies in mammals)
SINEs - 100 to 400 bp
AluI (one per 5,000 bp of human genome)
Tandem Repeats
Telomeric sequences - 1 - 10 bp long
rRNA and tRNA genes -