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BIOB11H3 Study Guide - Midterm Guide: Radioactive Tracer, Ionic Strength, Genome Size


Department
Biological Sciences
Course Code
BIOB11H3
Professor
Dan Riggs
Study Guide
Midterm

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BIOB11-L1: DNA, Genome Organization and Molecular Evolution
Timeline
1865 Discovery of discrete units of inheritance (Peas)
1880 Discovery of chromosomes
1903 Discovery of homologous chromosomes
1909 Discovery of crossing over
1911 Discovery that genes could be mapped in order along length of chromosomes
1944 Discovery of DNA as genetic material
1953 Discovery of DNA structure
2017 Many genomes completely sequenced, “Bioinformatics/ Computational genomics” comes of age
Mendel
Used plants (peas) with complete flowers (with both male & female reproductive structures)
- Most organisms are DIPLOID: two copies of each gene
- Allele: Alternative forms of the same gene
- Genotype: Genetic composition of the organism
Pollen contains sperm Carpel may contain many ovules (containing eggs) Multiple fertilization events occurs
Genotype: Genetic composition of the organism
Phenotype: Observable traits or morphology of seeds
Homozygous: Both alleles are identical (RR “wildtype”)
Heterozygous: Alleles differ (One dominant, one recessive Carrier)
Nulls: Homozygous recessive (rr “mutant”)
Heterozygote example: Mother donates normal gene and Father donates mutant gene Heterozygous progeny OFTEN exhibits “normal” activity
The Search for the “Heredity Molecule”
DNA Polymer: Only 4 nitrogenous bases
Protein Polymer: 20 different AA building blocks
(Proteins are much more complex, but turns out its DNA that is the genetic material)
Landmark Experiments
1. Studies of virulent strains of showed that a “transforming principle” could be passed from one bacteria to another, and that DNA carries
the information
2. Studies of viruses that infect bacteria (bacteriophage / ‘phage’), proved that phage DNA (NOT PROTEIN) was responsible for the viral
infection
Griffiths Showed that heat killed and lysed bacteria (Streptococcus) contained a ‘transforming principle’ (TP)
- Encapsulated strains virulent (Capable of causing disease)
- Capsuleless strains non-virulent
Some soluble factor must be taken up by the live capsules (R) cells to
transform them into virulent encapsulated (S) strain
Avery, McCarty & McLeod postulated the TP was DNA based on:
1. Chemical properties of the TP were consisted with it being DNA.
2. No other type of material could be detected in preparation
Steps: Encapsulated strain Lyse cell, filter to obtain cell free extract Use enzymes that degrade a specific macromolecule (e.g. DNAse for DNA)
Use the altered extract to determine if it retained the transforming property
Result: Only DNAse enzymes could inactivate the Transforming Principle, hence DNA is the genetic material
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