Principles of Genetics: Biotechnology and Molecular Techniques

Requirements for Genetically Modifying an Organism: * Obtain the gene of interest in high copy numbers. * Develop a mechanism to insert the gene into the target cells. * Establish a way to verify that the cells successfully received the gene. * Ensure that the inserted gene is appropriately expressed within the cell. * Develop a method to confirm that the sequence entered the genome intact.

Sanger Sequencing (Dideoxy Sequencing): * Uses dideoxynucleotides (ddNTPs) which lack an $-OH$ group on the $3'$ carbon atom. * Functional Consequence: Because there is no $3'$ hydroxyl group, no additional nucleotides can be added to the DNA chain. * Terminator Nucleotides: These molecules act as terminators, stopping DNA synthesis at specific points to allow for fragment analysis.
Next Generation Sequencing (NGS): * Multiplexing: NGS allows for the sequencing of many thousands or millions of targets simultaneously. * Comparison: While dideoxy sequencing is typically limited to a single target per reaction, NGS is high-throughput and can sequence many targets at once.

Microsatellites: * Also known as Short Tandem Repeats (STRs). * Consist of variable numbers of copies of repeat sequences possessed by many organisms.
Detection Method: * STRs are detected using Polymerase Chain Reaction (PCR). * The resulting DNA fragments are represented as peaks on a graph for analysis.
Genotypic Peak Patterns: * Homozygotes: Represented by a single tall peak on the graph. * Heterozygotes: Represented by two shorter peaks on the graph.
Forensic and Identification Applications: * DNA fingerprinting is used to determine if a suspect was present at a crime scene. * Notable Application: Used in identifying people who died in the collapse of the World Trade Center. * CODIS (Combined DNA Index System): Uses 13 specific STR loci for DNA fingerprinting (Source: J. M. Butler and C. R. Hill, Forensic Science Review 24:15–26, 2012).

Forward Genetics: * Focuses on the transition from phenotype to genotype. * Begins with a specific phenotype and seeks to identify the gene that encodes it.
Reverse Genetics: * Focuses on the transition from genotype to phenotype. * Begins with a gene of unknown function, induces mutations in it, and then observes the resulting effect on the organism's phenotype.

Targeted Mutagenesis: A technique used to increase the number of mutants in an experimental population to study gene function.
Mutagenic Agents: * Radiation. * Chemical mutagens. * Transposable elements.
Key Systems and Methods: * CRISPR-Cas9 system: A modern tool for precise genome editing. * Site-directed mutagenesis: Employs restriction enzymes to target specific areas. * Oligonucleotide-directed mutagenesis: Specifically utilized when appropriate restriction sites are not available for experimental manipulation.

Transgenic Animals: * Definition: An organism that has been permanently altered by the addition of a DNA sequence to its genome through recombinant DNA technology. * Transgene: The specific gene or gene fragment that is permanently inserted into the target genome. * Example: Mice can be made transgenic for mutations that cause obesity.
Knockout and Knock-in Mice: * Knock-out mice: Animals in which a normal gene has been fully disabled to observe the loss-of-function effect. * Knock-in mice: Animals that carry an inserted DNA sequence at a specific, targeted location in the genome.

siRNAs (Small Interfering RNAs): * Process called RNA interference (RNAi). * Trans Effects: RNAi effects occur in trans, meaning they affect both copies of the targeted gene. * Durability: The effects are reversible and, by definition, do not last long.
Production: siRNAs can be produced by cloning DNA sequences corresponding to the siRNAs between two strong promoters.
Human Disease Treatment and Research: * High Cholesterol: RNAi has been used to target the ApoB protein. * Experimental Evidence: The transfer of siRNAs for the ApoB protein into cynomolgus monkeys significantly lowered blood-cholesterol levels.

Somatic Gene Therapy: * Modifies genes only in somatic (non-reproductive) tissue. * These modifications cannot be inherited by offspring.
Germ-line Gene Therapy: * Alters genes in germ-line cells (sperm or eggs). * These alterations have the potential to be passed on to future generations.