Biotechnology Terms Starting With M

Marker-Assisted Selection is a plant and animal breeding technique that uses DNA markers linked to desirable trait loci to identify and select individuals carrying target genes without requiring full phenotypic evaluation.

Marker-assisted selection accelerates crop improvement by identifying superior genotypes at the seedling stage rather than waiting for mature plants to express traits, compressing breeding cycles from roughly 10 years to 5 years in many programs. PCR-based markers such as simple sequence repeats and single nucleotide polymorphisms located within or flanking genes of interest are scored from microgram quantities of leaf DNA. Rice breeders at the International Rice Research Institute combined eight disease and stress resistance loci into single varieties using MAS, a feat nearly impossible with conventional phenotypic selection because it would require simultaneously challenging plants with multiple pathogens and abiotic stresses.

The technology proves especially valuable for traits that are expensive or slow to measure directly, such as grain protein content requiring wet chemistry or submergence tolerance requiring controlled flooding trials. Some wheat programs now screen more than 30,000 individual plants per week using automated MAS pipelines that extract DNA from single seeds.

Microarray is a solid support, typically a glass slide or silicon chip, containing thousands of microscopic DNA, RNA, or protein spots arranged in a grid for the parallel analysis of gene expression or genetic variation across an entire sample.

Affymetrix pioneered commercial DNA microarrays in 1994, using photolithography to synthesize oligonucleotide probes directly on silicon wafers and achieving spot densities exceeding one million features per square centimeter. Typical expression experiments involve labeling sample RNA with fluorescent dyes, hybridizing labeled targets to complementary probes on the array, then scanning to quantify binding intensity at each spot. This approach enabled simultaneous measurement of expression levels for more than 40,000 genes on a single slide smaller than a standard microscope slide.

Landmark applications include the molecular classification of breast cancer into distinct subtypes by Perou and colleagues in 2000 and the identification of gene expression signatures predicting chemotherapy response. Despite partial displacement by RNA sequencing, microarrays remain cost-effective for targeted studies, with per-sample costs under 50 dollars compared to roughly 500 dollars for RNA-seq, and they continue to appear in more than 5,000 published studies annually.

Monoclonal antibody is a laboratory-produced protein that binds with high specificity to a single epitope on a target antigen, generated from a clonal population of identical immune cells.

Monoclonal antibodies are produced by fusing an antigen-stimulated B cell with an immortal myeloma cell to create a hybridoma, a technique developed by Georges Köhler and César Milstein in 1975 for which they received the Nobel Prize in Physiology or Medicine in 1984. Each hybridoma clone secretes antibodies with a single defined binding specificity, allowing researchers to produce unlimited quantities of a chemically uniform protein. Early therapeutic monoclonal antibodies were derived entirely from mouse sequences and triggered immune reactions in human patients; modern engineering strategies such as humanization and fully human antibody phage display libraries have largely eliminated this problem.

Trastuzumab, approved by the FDA in 1998, targets the HER2 receptor overexpressed in roughly 20 percent of breast cancers and reduces recurrence risk by approximately 50 percent when combined with chemotherapy. More than 100 monoclonal antibody drugs are now approved in the United States, spanning oncology, autoimmune disease, and infectious disease indications.

mRNA Vaccine is a type of vaccine that delivers synthetic messenger RNA encoding a pathogen-derived antigen into human cells, directing ribosomes to produce that antigen and stimulate a protective immune response.

Once injected, the mRNA is taken up by cells at the injection site and in nearby lymph nodes, where ribosomes translate it into the target antigen protein, typically within hours. Lipid nanoparticles, the delivery vehicles used in the Pfizer-BioNTech and Moderna COVID-19 vaccines, protect the mRNA from degradation by serum ribonucleases and facilitate endosomal escape into the cytoplasm. The mRNA does not enter the nucleus, cannot integrate into chromosomal DNA, and degrades within days after translation is complete.

Katalin Karikó and Drew Weissman demonstrated in 2005 that substituting pseudouridine for uridine in synthetic mRNA dramatically reduced the innate immune activation that had previously made mRNA therapeutics impractical, a discovery recognized with the 2023 Nobel Prize in Physiology or Medicine. Clinical development of mRNA vaccines began years before COVID-19, with candidates targeting rabies, influenza, Zika virus, and personalized cancer neoantigens advancing through early-phase trials.