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IB Biology: Topic 3.5
3
IB Biology: Topic 3.5
by marco
What is PCR?
PCR
- polymerase chain reaction (PCR)
- an artificial method of replicating DNA under laboratory conditions
- a technique used to amplify large quantities of a specific sequence of DNA from an initial minute sample
- each reaction cycle doubles the amount of DNA
1. Denaturation - DNA sample is heated to separate it into two single strands
2. Annealing - DNA primers attach to the 3 ends of the target sequence
3. Elongation - a heat tolerant DNA polymerase which binds to the primer and replicates the strand
Stages of PCR
PCR components
What is gel electrophoresis?
Gel electrophoresis
- a laboratory technique used to separate and isolate proteins or DNA fragments based on mass or size
- samples are placed in a block of gel and an electrical current is applied causing the samples to move through the gel
- smaller samples are less impede by the gel matrix and hence will travel faster through the gel
- causing samples of different sizes to separate as they travel at different speeds
DNA Separation
- DNA may be cut into fragments using restriction endonuclease – different DNA samples will generate different fragment lengths
- Fragments separate because DNA is negatively charged because of the presence of a phosphate group on each nucleotide
- DNA samples are placed into an agarose gel and fragment size calculated by comparing against current industry standards
- Specific sequences can be identified by using a complementary radiolabelled hybridisation probe, transferring the separated sequences to a membrane and then visualising through autoradiography
Polyacrylamide Gel Electrophoresis
What is DNA profiling?
DNA Profiling
- a technique which inviduals can be identified and have their DNA compared using their DNA profiles
- satellite DNA (long stretches of DNA made up of repeating elements) exists within the non-coding regions of someone's genome
- As individuals will likely have different numbers of repeats at a given satellite DNA locus, they will generate unique DNA profiles
Example 1 (Forensic Investigation)
Suspects should be a complete match with the DNA sample taken from the crime scene for them to be convicted of the crime
The number of loci used to produce a unique profile depends on the size of the population which is being compared
Example 2 (Paternal Testing)
Children inherit half their chromosomes from each parent and therefore should possess a combination of parental fragments
Criminal Investigations and to settle paternity disputes
Application
Similar procedure for both:
- DNA sample is collected and then amplified using PCR
- Satellite DNA are cut to generate fragments
- fragments are separated using gel electrophoresis, profiles remaining are compared
What is Gene Transfer?
Gene Transfer
- a gene determines a particular trait by encoding for a specific polypeptide
- Due to the genetic code being nearly universal, an organism can potentially express a new trait if the suitable gene is introduced into its genome
- the transfer of genes between species is called gene modification - the new organism created is called a transgenic
Bacteria producing human Insulin
The 4 Steps:
Gene transfer to bacteria using plasmids
1. Isolation of gene and vector (by PCR)
2. Digestion of gene and vector (by restriction endonuclease)
3. Ligation of gene and vector (by DNA ligase)
4. Selection and expression of transgenic construct
- Gene transfer to bacteria using plasmids makes use of restriction endonucleases and DNA ligase
What is natural cloning?
Natural Cloning
- Many plant species and some animal species have natural methods of cloning
- All bacteria, the majority of fungi and multiple species of protists reproduce asexually producing genetic clones
- While most plants reproduce sexually, they are also able to asexually reproduce
Animal Cloning Methods
1. Binary Fission
2. Budding
3. Fragmentation
4. Pathenogesis
Animal Cloning
Binary Fission
- parent organism splits in two, producing two genetically identical daughter organisms
- this method of cloning occurs in Planaria and is also common to bacteria and protists
Budding
- Cells split off the parent organism, which generates a smaller daughter organism that eventually separates from the parent
- This method of cloning occurs in Hydra and is also common to many species of yeast
Fragmentation
- New organisms grow from a separated fragment of the parent organism
- this method of cloning is common to starfish and certain species of annelid worms
Pathenogesis
- Embryos are formed from unfertilised ova
- This method of cloning occurs in certain species of insect, fish, amphibians and reptiles
Plant Cloning Methods
1. vegetative propagation
2. asexual reproduction (through spores)
Plant Cloning
Vegetative Propagation
Plants have the capacity for vegetative propagation - small pieces are induced and then are able to grow independently
Asexual reproduction (through spores)
- some plants (mainly algae, mosses and ferns) can reproduce asexually by producing spores
- spores are also produced by certain types of bacteria and fungi
Human Cloning Methods
Human Cloning
1. Identical twinsare created when a fertilised egg splits into two identical cells, each forming an embryo
2. Non-identical twins are created when an unfertilised egg splits into two cells and each is fertilised by a different sperm
Monozygotic
- genetically identical
Dizygotic
- 50% of DNA is the same
What is artificial cloning?
Artificial cloning
- Animals can be cloned at the embryo stage by breaking up the embryo into more than one group of cells
- If these embryonic cells are separated artificially, each group of cells will form cloned organisms
- the separation has to happen early in the developmental cycle around the 8 cell stage
Embryonic division
Reproductive and Therapeutic cloning
reproductive - if the embryo is implanted into the uterus of a surrogate, a new cloned organism will develop
therapeutic - Embryonic cells can be induced to differentiate to create specific tissues or organs used for transplantation
What are clones?
Clones
- Clones are groups of genetically identical organisms, derived from a single original parent cell
- Organisms that asexually reproduce will produce genetically identical clones
- mechanisms exist whereby sexually reproducing organisms can produce clones
Somatic Cell Nuclear Transfer
Somatic cell nuclear transfer is a method by which cloned embryos can be produced using differentiated adult cells
https://ib.bioninja.com.au/standard-level/topic-3-genetics