Chapter 12: DNA Technology

Chapter 12: DNA Technology

Introduction: Are More Genes Better?

Humans have about the same number of genes as a microscopic worm and only half as many as a rice plant. This surprising fact highlights that gene number does not directly correlate with organismal complexity.

• Gene count: Humans (~21,000 genes), rice plant (~40,000 genes), microscopic worm (similar to humans).

• Implication: Complexity arises from gene regulation and interactions, not just gene number.

Biology and Society: Using DNA to Establish Guilt and Innocence

DNA Profiling in Forensics

DNA profiling is the analysis of DNA samples to determine whether they originate from the same individual. It is a powerful tool in forensic science and legal investigations.

• Evidence: DNA technology can provide evidence of guilt or innocence.

• Historical case: Used to confirm the identity of the Boston Strangler decades after the crimes.

Societal Impacts of DNA Technology

• Genetically Modified (GM) Crops: Engineered to produce their own insecticides.

• Comparative Genomics: Human genes compared with those of other animals to understand human uniqueness.

• Medical Advances: Detection and treatment of fatal genetic diseases.

Genetic Engineering and Biotechnology

Biotechnology: Definition and History

Biotechnology is the manipulation of organisms or their components to make useful products. It dates back to ancient times (e.g., yeast for bread and beer, selective breeding of livestock).

• Modern biotechnology: Involves DNA technology and laboratory techniques for studying and manipulating genetic material.

Genetically Modified Organisms (GMOs) and Transgenic Organisms

• GMOs: Organisms that have acquired one or more genes by artificial means.

• Transgenic organisms: Recombinant organisms with genes from another species.

Recombinant DNA Technology

Recombinant DNA is constructed by combining DNA from two different sources, often different species, to form a single DNA molecule.

• Genetic engineering: Direct manipulation of genes for practical purposes.

• Applications: Mass production of chemicals (e.g., cancer drugs, pesticides), gene transfer between species.

• Example: Glowing fish produced by transferring a jellyfish gene for fluorescent protein.

Recombinant DNA Techniques

Bacterial Plasmids and Gene Cloning

Bacteria are essential tools in biotechnology. Plasmids are small, circular DNA molecules that duplicate independently of the bacterial chromosome.

• Plasmids: Can carry any gene and are passed between bacterial generations.

• Gene cloning: Production of multiple identical copies of a gene-carrying DNA piece.

How to Clone a Gene

Gene cloning is used to manufacture proteins on a large scale, such as drugs. The process involves identifying a gene of interest, inserting it into a plasmid, and using bacteria to produce the protein.

• Steps: Isolate gene, insert into plasmid, transform bacteria, grow bacteria, harvest protein.

Gene Editing: The CRISPR-Cas9 System

CRISPR-Cas9 Technology

CRISPR-Cas9 allows precise editing of specific genes in living cells. It is a revolutionary tool for genetic engineering.

• Function: Can reveal gene function or correct mutations.

• Mechanism: Cas9 protein cuts DNA at a site specified by guide RNA.

• Applications: Gene knockout, mutation correction (e.g., Duchenne muscular dystrophy in mice).

Checkpoint: Guide RNA directs Cas9 to the target DNA sequence for cutting.

Medical Applications of DNA Technology

Production of Useful Proteins

Genes for desired proteins are transferred into bacteria, yeast, or other cells to produce large quantities of proteins.

• Humulin: Human insulin produced by genetically modified bacteria.

• Other products: Human growth hormone (HGH), blood clot-dissolving proteins, vaccines, erythropoietin (EPO).

• Transgenic animals: Used to produce drugs (e.g., lysozyme in goats).

Checkpoint: Yeast are used for some human proteins because they can perform post-translational modifications that bacteria cannot.

Genetically Modified Organisms in Agriculture

Applications in Crop and Animal Improvement

DNA technology is replacing traditional breeding to improve productivity and traits in crops and animals.

• GM crops: Corn, soybean, cotton in the U.S. are mostly genetically modified.

• Traits: Insect resistance, cold tolerance (antifreeze proteins in strawberries), edible vaccines (cholera proteins in potatoes and rice).

• GM animals: Atlantic salmon engineered for rapid growth and larger size.

Human Gene Therapy

Gene Therapy Approaches

Gene therapy treats disease by introducing genes into affected individuals.

• Replacement: Mutant gene replaced or supplemented with normal allele.

• Temporary expression: Genes inserted for short-term treatment.

• Example: Use of bone marrow stem cells as targets for gene therapy due to their ability to regenerate blood and immune cells.

DNA Profiling and Forensic Science

DNA Profiling Techniques

DNA profiling compares variable sequences in the genome to identify individuals.

• Polymerase Chain Reaction (PCR): Amplifies specific DNA segments for analysis.

• Short Tandem Repeat (STR) Analysis: Compares lengths of repeated DNA sequences at specific sites.

• Gel Electrophoresis: Separates DNA fragments by size for comparison.

Technique	Main Purpose
PCR	Amplify DNA segments
STR Analysis	Compare repeat lengths at specific loci
Gel Electrophoresis	Sort DNA fragments by size

Genomics and the Human Genome Project

Genomics: Study of Whole Genomes

Genomics investigates complete sets of genes (genomes) in organisms.

• Human Genome Project: Sequenced all human DNA, identified gene locations and sequences.

• Findings: Humans have ~21,000 genes; reference genome compiled from multiple individuals.

• Comparative genomics: Revealed evolutionary relationships (e.g., humans share 96% of genome with chimpanzees).

• Ancient DNA: Neanderthal genome sequenced, showing interbreeding with modern humans.

Safety, Ethical, and Societal Issues

Safety Concerns

• Risks: Creation of hazardous organisms, transfer of harmful genes.

• Regulation: Strict laboratory procedures and government guidelines.

Controversy over Genetically Modified Foods

• Global impact: GM foods are major staples in several countries.

• Debate: Safety, environmental impact, mandatory labeling, gene transfer to wild relatives.

• Biosafety Protocol: International agreement for identifying and regulating GM organisms in food shipments.

Ethical Questions Raised by Human DNA Technologies

• Genetic defects: Should we eliminate them in future generations?

• Genetic diversity: Essential for adaptation; some genes may be beneficial in changing environments.

• Privacy: DNA profiling and personal genetic information raise privacy and discrimination concerns.

• Legislation: Genetic Information Nondiscrimination Act (2008) protects against misuse in insurance and employment.