Table of Contents
Overview
Genetic engineering methods make it possible not only to analyze DNA, but also to modify it in targeted ways. These techniques are applied in many areas of everyday life and research. This chapter focuses on where and why genetic methods are used, what goals are pursued, and which practical examples are important—without going into the technical details of the methods themselves.
General Purposes of Applied Genetics
Genetic methods are used to:
- understand biological processes (basic research),
- diagnose and monitor diseases,
- improve or protect human, animal, and plant health,
- increase yields or desirable traits in agriculture and industry,
- produce substances (e.g. medicines, enzymes) biotechnologically,
- clarify relationships and identity in forensics,
- conserve biodiversity and manage wild populations.
The same methodological toolbox can be used for very different purposes; the difference lies in which organisms are modified or analyzed and what the end goals are.
Medicine and Human Health
Diagnostic Applications
Genetic diagnostics aim to detect changes in DNA or gene activity relevant to disease.
Detection of Hereditary Diseases
- Carrier tests identify whether a healthy person carries a mutation that can be passed on (e.g. cystic fibrosis, sickle cell disease).
- Predictive tests estimate the risk of developing a genetic disease later in life (e.g. certain forms of breast cancer, Huntington’s disease).
- Prenatal and preimplantation genetic diagnosis examine embryonic/fetal cells for specific genetic alterations.
These tests usually search for:
- known mutations in specific genes,
- characteristic changes in chromosome number or structure,
- patterns of gene expression (which genes are active or inactive).
Diagnosis of Infectious Diseases
Instead of detecting pathogens indirectly (e.g. antibodies), genetic methods can detect pathogen nucleic acids directly:
- rapid identification of viruses and bacteria (e.g. SARS‑CoV‑2, HIV, tuberculosis),
- detection of antibiotic resistance genes,
- differentiation between related strains in outbreaks (molecular epidemiology).
Pharmacogenetics and Personalized Medicine
People differ in how they metabolize or respond to drugs. Genetic analyses can:
- identify variants in genes for drug‑metabolizing enzymes,
- predict whether a drug will be effective or cause side effects,
- help select the right drug and dose (“personalized” or “precision” medicine).
Examples:
- Choice and dosage of certain blood thinners or cancer drugs based on genetic variants.
- Avoiding drugs that a person cannot metabolize safely.
Gene‑Based Therapies and Cell Therapies
While the methods and principles are treated elsewhere, here the main application areas:
- Monogenic diseases: Attempts to correct or compensate for a defective gene (e.g. certain immune deficiencies, some forms of inherited blindness).
- Cancer therapy:
- Transfer of genes into immune cells to better recognize and destroy tumor cells (e.g. CAR‑T cell therapies).
- Use of genetically modified viruses (oncolytic viruses) that preferentially infect and kill tumor cells.
- Regenerative medicine: Combination of genetic modification with stem cells to repair tissues or organs.
These therapies often distinguish between:
- Somatic gene therapy: affects only body cells of the treated person; not inherited.
- Germline modification: affects egg/sperm or early embryo cells; the change would be heritable. This is highly controversial and largely prohibited in humans in many countries.
Production of Pharmaceuticals
Genetically modified organisms (GMOs) are widely used as “cell factories” to produce:
- Hormones (e.g. human insulin from bacteria or yeast),
- Clotting factors and other blood proteins,
- Growth factors and cytokines,
- Monoclonal antibodies (e.g. for cancer or autoimmune diseases),
- Vaccines (e.g. proteins from pathogens produced in yeast, insect, or mammalian cells).
Advantages over older methods:
- higher purity and safety (no need for large amounts of human or animal tissue),
- scalable industrial production,
- ability to modify molecules (e.g. more stable, more effective variants).
Agriculture and Food Production
Genetic applications in agriculture aim to stabilize or increase yields, reduce losses, and alter product properties.
Genetically Modified Crop Plants
Genetically modified (GM) plants are used for:
- Pest resistance: e.g. plants expressing bacterial Bt toxins against certain insect larvae.
- Herbicide tolerance: enabling use of specific herbicides without killing the crop.
- Disease resistance: resistance to viruses, fungi, or bacteria via introduced genes.
- Stress tolerance: improved tolerance to drought, salinity, or cold.
- Quality traits:
- altered oil composition,
- delayed ripening and longer shelf life,
- modified starch or protein composition,
- increased content of vitamins or micronutrients (“biofortification”).
Some GM crops combine multiple traits (“stacked” varieties).
Genetically Modified Farm Animals
Application to animals is more technically demanding and ethically sensitive than in plants. Examples and goals:
- Increased productivity: growth or milk yield (now controversial; some projects discontinued).
- Disease resistance: e.g. pigs resistant to certain viral diseases.
- Compositional changes: altered milk or meat composition (e.g. more unsaturated fatty acids).
- Bioreactors: animals producing pharmaceuticals in milk, eggs, or blood.
In practice, only a few GM animal lines have been approved for food; others are used mainly in research or for pharmaceutical production.
Food Enzymes, Additives, and Processing Aids
Even when the final food does not contain GM organisms, genetic engineering may be involved:
- Enzymes (e.g. chymosin for cheese making, amylases and proteases for baking or brewing) produced by GM microorganisms.
- Vitamins and amino acids produced via genetically modified bacteria or yeasts.
- Flavor compounds and food additives produced biotechnologically.
In many countries, labeling regulations distinguish between foods “made from” GMOs and foods produced “with the help of” GM microorganisms that are removed from the final product.
Environmental and Industrial Biotechnology
Bioremediation and Environmental Protection
Genetic methods can help remove or reduce environmental pollutants:
- microorganisms engineered to degrade oil, pesticides, or industrial chemicals more efficiently,
- bacteria able to accumulate heavy metals to clean contaminated sites,
- plants (“phytoremediation”) enhanced to take up or transform toxins.
Field use is strictly regulated to minimize ecological risks and unintended spread.
Industrial Production of Chemicals and Materials
Genetically modified microbes are used in:
- Production of bulk chemicals (e.g. organic acids, solvents),
- Biofuels (e.g. ethanol, butanol, biodiesel precursors),
- Bioplastics (e.g. polyhydroxyalkanoates),
- Detergent enzymes working at specific temperatures or pH.
Compared to purely chemical synthesis, these processes can:
- use renewable raw materials (e.g. plant sugars),
- operate at lower temperatures and pressures,
- reduce toxic by‑products.
Research, Model Organisms, and Functional Genomics
Model Organisms
Much of our knowledge about genes and their functions comes from genetically modified model organisms:
- Bacteria and yeast for basic molecular biology.
- Fruit flies, nematodes, zebrafish, mice for studying development, behavior, and disease.
- Arabidopsis and other plants for plant genetics.
Genetic modifications allow:
- targeted switching off (knock‑out) or activation (overexpression) of genes,
- insertion of reporter genes (e.g. fluorescence) to visualize processes,
- modeling of human diseases to test interventions.
Functional Analysis of Genes and Genomes
Genetic tools are applied to:
- systematically study the function of thousands of genes (“functional genomics”),
- map regulatory networks and signaling pathways,
- track cell lineages during development (genetic barcoding),
- study evolution by comparing gene sequences and functions across species.
These research applications often indirectly drive medical and technological innovations.
Forensic and Legal Applications
Forensic DNA Analysis
Genetic methods are used in criminal investigations and disaster victim identification:
- comparison of DNA profiles from traces (hair, blood, saliva) with reference samples,
- identification of unknown bodies via relatives,
- linking suspects, victims, and crime scenes.
Typically, non‑coding, highly variable DNA regions (short tandem repeats, STRs) are analyzed; these are useful for identification but usually not informative about traits or diseases.
Paternity and Kinship Testing
Genetic markers allow:
- paternity and maternity testing,
- clarification of kinship (e.g. siblings, grandparent‑grandchild),
- verification of family relationships in legal and immigration contexts.
Statistical evaluation shows how likely a given relationship is, based on the pattern of inherited markers.
Wildlife Forensics and Trade Control
Applications outside human law:
- identification of protected species in confiscated goods (e.g. ivory, bushmeat, traditional medicines),
- tracing the origin of timber or fish products,
- combating illegal trade in endangered species.
Conservation Biology and Population Management
Monitoring Genetic Diversity
Genetic markers help:
- assess genetic diversity within and between populations,
- detect inbreeding and loss of diversity in small or isolated populations,
- identify distinct populations or subspecies that require tailored protection.
This information supports decisions on:
- establishing protected areas,
- planning corridors between habitats,
- prioritizing populations for conservation.
Reintroduction and Breeding Programs
For endangered species, genetic analyses guide:
- choice of breeding pairs in zoos or breeding stations to minimize inbreeding,
- selection of individuals for reintroduction that best represent the original gene pool,
- monitoring of whether reintroduced populations interbreed with wild ones and maintain diversity.
Management of Exploited Populations
In fisheries and wildlife management, genetics can reveal:
- whether harvest levels are sustainable,
- hidden population structure (distinct stocks) that should be managed separately,
- illegal catches from protected populations.
Ethical, Legal, and Social Aspects of Applications
The applications of genetics raise questions beyond pure biology:
- Safety: risk assessment for GMOs in the environment and food chain.
- Data protection: handling of genetic information in medicine and forensics.
- Justice: fair access to genetic diagnostics and therapies.
- Consent and autonomy: especially for predictive tests and germline interventions.
- Biodiversity and ecology: unintended effects of gene flow and species modification.
Many countries have specific laws and regulatory agencies for:
- approval and monitoring of GMO use,
- biosafety in laboratories and industry,
- data protection in genetic testing,
- oversight of clinical trials involving gene‑based therapies.
Understanding these dimensions is essential for responsible use of genetic technologies in all application fields described above.