Study Guides (390,000)
CA (150,000)
UTSC (10,000)
Biological Sciences (800)
BIOB11H3 (50)
Dan Riggs (30)
Midterm
Department
Biological SciencesCourse Code
BIOB11H3Professor
Dan RiggsStudy Guide
MidtermThis preview shows pages 1-3. to view the full 33 pages of the document.
BIOB11: MOLECULAR CELLULAR AND GENETIC PRACTICAL WINTER 2018
BIOB11
Lecture 1
History of Genetics
• 1856→ discovery of unit of inheritance
o Mendel and his principles of hereditary
• 1880→ discovery of chromosomes
o With the use of the microscope
• 1903→ discovery of homologous chromosomes
• 1909-1911 → discovery of crossing over
o During meiosis the mom and the dad’s chromosomes cross over their different genes
• 1911-1913 → genes can be mapped in order along the length of the chromosome
• 1944-2952→ DNA is the genetic material, not proteins
• 1953 → DNA structure by Watson and crick
• In 2018 many genomes are completely sequenced and can be done quickly
o Human genomes are 3x 10 ^9 bp, and now take a day to do
o Bioinformatics/computational genomics
Diploid
• Most organisms are this
• There are two copies of each gene and chromosome
Allele
• Alternative forms of the same gene
Genotype
• The genetic composition of the organism
Phenotype
• The observable traits or morphology of seeds
• Based on which trait is dominant
Mendel
• When Mendel was establishing the basis of heredity, he used
height, colour, and shape alleles
• He was able to determine that some traits were dominant over
others
• He used peas that had complete flowers →with both male and
female reproductive structures
o Anthers shed Pollen that contains the sperm
o Carpel contains ovules which contain eggs
o There can be multiple fertilization events
o In peas multiple ovules an be fertilized by a pollen grain
• The pea pods contained 8-10 seeds/progeny
• The plants were allowed to self fertilize, he used a punnet square
to determine the traits of sperm vs egg
• He observed that two alleles are segregating and that one has
dominance on the other
Homozygous
• When both alleles are the same (dominant or recessive)
• Wildtype → the homozygous dominant
o The most prominent in the population, purebred for dominant phenotype
• Nulls → Homozygous recessive
Only pages 1-3 are available for preview. Some parts have been intentionally blurred.
BIOB11: MOLECULAR CELLULAR AND GENETIC PRACTICAL WINTER 2018
o This is generally associated with a mutant trait
o Pure breeding that gives rise to the recessive/mutant trait
Heterozygous
• When the alleles are different (dominant and recessive)
• Not pure breeding, the next generation can have both phenotypes
Heterozygote Example
• Suppose mother donates normal dominant genes and father donates recessive mutant genes, the heterozygous
progeny will often exhibit normal activity
• The mutated gene will be translated and transcribed and will lead to an inactive protein, but the dominant allele
will lead to an active protein
o As long as you have one good copy of the gene of the protein, you are ok
o But if both alleles have mutations you have problems and cannot produce the right protein and then you
are in trouble
• You are technically a carrier of the dads mutant gene even if you don’t express it
THE SEARCH FOR THE HEREDITARY MOLECULE
1900-1040
• Biochemists Characterize cellular macromolecules
• DNA is a polymer that has four nitrogen bases
• Proteins are polymers made of 20 amino acids
o Since proteins were more complex, they thought that was the genetic material
• They were both abundant in the cell
Evidence that DNA is the Genetic Material
• Avery, McCarthy and McLeod (1940)
o Studies of virulent strains of bacteria showed that a transforming principle could be passed from one
bacteria to another and that DNA may be the transforming principle that carries the information
o They said the transforming principle was DNA based on:
▪ Chemical properties of the transforming principle were consistent with DNA
▪ No other material could be detected in the preparation
o Experiment using a Direct Test
1. Encapsulated strain
2. Lyse cells, filter to obtain cell free extract (had all the insides)
3. Use enzymes that degrade a specific macromolecule (DNAse, proteinase etc.) into the extract
4. Inject mice with the altered extract to determine if it retained the transforming property
o The result was that only the DNAse enzymes could inactivate the transforming principle, so DNA is
therefore the genetic material
o If you used the protease, the mouse still got the infection, therefore the transforming principle was still
present so it couldn’t have been proteins
• Hershey and Chase (1950)
o Studied viruses that infect bacteria and proved that phage DNA was responsible for the viral infection
o Bacteriophage → virus that infects bacteria
▪ Contains a protein coat that encases the DNA
▪ It is released from a host cell and finds another new host cell that it can inject the DNA into and
it uses that cell to reproduce until it bursts and releases more phage
o Experiment
▪ The bacteriophage displays heritable properties
Only pages 1-3 are available for preview. Some parts have been intentionally blurred.
BIOB11: MOLECULAR CELLULAR AND GENETIC PRACTICAL WINTER 2018
▪ They wanted to know if the protein or DNA
directed the replication of the new
bacteriophage
▪ They radiolabelled the protein or DNA of a
bacteriophage and infected the bacteria
cells
▪ When the DNA was labelled, there was
radiolabel found in the bacteria/ new phage
DNA
▪ When the protein was labeled, the
radiolabel was found in empty phage
particles
o They too concluded that DNA was the genetic material because that is what caused the infection
• Griffiths
o Came before the Avery et al experiment
o Showed that heat killed lysed streptococcus pneumonia bacteria contained a transforming principle
o The encapsulated(s) strains were virulent, the capsuleless (r) strains are not virulent
▪ Inject live s cells→ mouse dies from infection
▪ Inject live r cell→ mouse lives
▪ Inject heat killed s cells → mouse lives
• This shows that heat can kill the contagious aspect
▪ Heat killed s cells and live r cells → mouse dies from infection
• When you combined the two non contagious trials, the mouse still died…. Why
• There must be a soluble factor that is released from the s cells to the r cells to transform
them into a virulent cells
o The transforming principle transformed harmless cells into virulent cells
o Therefore there must be some factor that can be taken up by the live r cells to transform them into the
virulent s cells→ transforming principle
• Watson, Crick, Wilkins and Franklin (1950)
o Used x-ray crystallography elucidate the structure of DNA
▪ You make crystals of the molecule, shine an x ray and the detraction of the x ray produces a
picture of the structure
DNA Structure
• It has a double stranded, antiparallel structure, 3’-5’ vs 5’3’, these refer to the carbon positions in the sugar
molecule that link adjacent bases in DNA
• Complementary base pairing occurs by hydrogen bonding of arginine to thymine and guanine to cytosine
o In RNA uracil replaces thymine
• Nucleotide → phosphate group, sugar, and nitrogenous base
• Nucleoside → the structure without the phosphate group
• The phosphate and sugar are connected by phosphodiester bonds
• Nitrogenous Bases
o Purines → arginine and guanine
o Pyrimidines → cytosine, thymine and uracil
Early Work on DNA: Physiochemical Approaches
• DNA is a polynucleotide chain
• Estimates made of genome size
• Values were tiny yet enormous
o Humans: 3.5 pictograms of DNA/haploid (3x 10 ^-12 grams)
You're Reading a Preview
Unlock to view full version