Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Gel electrophoresis is used to separate proteins or fragments of DNA according to size and charge. DNA molecules are negatively charged and migrate towards the positive electrode (anode).
PCR (Polymerase Chain Reaction) is used to amplify small amounts of DNA. The process involves three temperature-dependent stages: Denaturation at , Annealing at , and Elongation using polymerase at .
DNA profiling involves the comparison of DNA. In IB Biology, this often focuses on Short Tandem Repeats (), which are non-coding regions of DNA that vary in length between individuals.
Genetic modification is carried out by gene transfer between species. This is possible because the genetic code is universal; for example, the codon codes for Methionine in nearly all organisms.
Gene transfer to bacteria involves using restriction endonucleases to cut DNA at specific sequences (forming 'sticky ends'), and ligase to join the target gene into a plasmid vector.
Genetically modified organisms () like corn contain a gene from Bacillus thuringiensis that produces a toxin to kill pests, reducing the need for chemical insecticides but raising concerns about non-target species like Monarch butterflies ( ).
Clones are groups of genetically identical organisms, derived from a single original parent cell. Somatic Cell Nuclear Transfer () is a method used to produce cloned embryos by replacing the nucleus of an unfertilized egg with a diploid nucleus from a differentiated somatic cell.
📐Formulae
💡Examples
Problem 1:
A scientist starts a PCR reaction with double-stranded DNA molecules. Calculate the total number of DNA molecules present after complete cycles of amplification.
Solution:
Explanation:
The number of DNA molecules doubles with every cycle. The formula used is , where is the initial number of molecules () and is the number of cycles ().
Problem 2:
In DNA profiling, if the probability of a specific allele occurring in a population is , and a profile uses such independent loci, what is the probability of another random person having the exact same profile?
Solution:
or
Explanation:
Since the loci are independent, the product rule of probability is applied. The individual probabilities are multiplied together to find the frequency of the total genotype.
Problem 3:
Identify the tools required to create a recombinant plasmid containing a human insulin gene ().
Solution:
- Restriction endonucleases (to cut the gene and plasmid). 2. ligase (to join the sugar-phosphate backbones). 3. plasmids (acting as the vector).
Explanation:
Restriction enzymes create compatible 'sticky ends' through complementary base pairing, while ligase facilitates the formation of covalent phosphodiester bonds.