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Lecture 14

01:119:115 Lecture Notes - Lecture 14: Frederick Griffith, Embryology, Genetic Recombination

6 pages61 viewsFall 2018

Biological Science
Course Code
Stern Cardinale

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Biology 10/19
All about DNA
1. DNA is the genetic material
SEQ, CC DNA experiments
2. DNA structure
CC, HD DNA structure
3. DNA Replication
SEQ, HD DNA replication
Last time’s stuff:
Determining linkage:
Can tell from dihybrid test cross results.
If the parental genotype is expressed by 100% of the offspring, there is linkage.
If the parental genotype is expressed by 50% of the offspring, there is no linkage.
If the parental genotype is expressed by between 50 and 100% of the offspring,
there is incomplete linkage.
Genetic recombination: 2 mechanisms
Unlinked genes: Independent assortment
Linked genes: Crossing over (unless they are completely linked)
Today’s lecture
1. DNA is the genetic material
Chromosomes= DNA+prteins
DNA= deoxyribonucleic acid
4 monomers- nucleotides
Protein- 20 amino acids
General consensus- genes-proteins
A. Frederick Griffith
Bacteriologist and embryologist
Working on pneumonia vaccine
1st to show evidence against protein hypothesis.
His model organism: Streptococcus pneumoniae
Bacteria causes pneumonia in humans
Lethal to mice
2 strains:
- Smooth (has capsule-pathogenic)
- Rough (no capsule-nonpathogenic)
Griffith’s experiment
- Live smooth bacteria recovered from dead mice
- Demonstrated transformation: Change in genotype and
phenotype due to some factors.
What transformed the cells?
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What happens to proteins when heated?
Do proteins simultaneously go back to correct
Conclusion: DNA most likely carries the genes.
B. Avery, McLeod and McCarty
Lysed S cells
Separated components
Tested for transformation
C. Hershey and Chase
Used Bacteriophage T2
Bacteriophage: Virus that affects bacteria
Viruses are less complex than cells
2 main components: DNA/RNA and a protein coat.
Virus life cycle
Virus attaches to host cells
Something enters the cells
New viruses made
Cell lyses, viruses released
Experimental design:
Label 1 virus population with radioactive sulfur
Label second with radioactive phosphorus
Allow each to infect bacteria
Separate viruses from bacteria
Determine location of radioactive isotopes.
Hershey and chase: Results:
Radioactive Sulphur in separated virus
Radioactive phosphorus present in infected cells.
Conclusion: Viruses transmit DNA; DNA carries genes
II. DNA structure
A. Nucleotides: monomers of nucleic acids. (FIG. 16.5)
Nitrogenous bases:
1. Purines: 2 rings
- Adenine
- Guanine
2. Pyrimidines: 1 ring
- Cytosine
- Thymine
DNA strand (16.5)
B. Determining DNA structure:
o Published in 1953 by James Watson and Francis Crick
o Much work done by others
Erwin Chargaff
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