M

Macrorestriction Map:

Map depicting the order of and distance between sites at which restriction enzymes cleave chromosomes.

M13:

A bacteriophage which infects certain strains of E. coli. The salient feature of this phage is that it packages only a single strand of DNA into its capsid. M13 is often used to generate templates for DNA sequencing.

Macrorestriction Map:

Map depicting the order of and distance between sites at which restriction enzymes cleave chromosomes.

Maintenance Methylase:

An enzymatic activity responsible for maintaining the patterns of methylation on each strand of a DNA molecule after replication.

Mapping:

See gene mapping, linkage map, physical map.

Marker:

Two typical usages:

1] Molecular Weight Size Marker: a piece of DNA of known size, or a mixture of pieces with known size, used on electrophoresis gels to determine the size of unknown DNA's by comparison.

2] Genetic Marker: An identifiable physical location on a chromosome (e.g., restriction enzyme cutting site, gene) whose inheritance can be monitored. Markers can be expressed regions of DNA (genes) or some segment of DNA with no known coding function but whose pattern of inheritance can be determined. See RFLP, restriction fragment length polymorphism.

Megabase (Mb):

Unit of length for DNA fragments equal to 1 million nucleotides and roughly equal to 1 cM.

Melting:

The dissociation of a duplex nucleic acid molecule into single strands, usually by increasing temperature.

Meiosis:

The process of two consecutive cell divisions in the diploid progenitors of sex cells. Meiosis results in four rather than two daughter cells, each with a haploid set (1n) of chromosomes.

Messenger RNA (mRNA):

Proteins are not synthesized directly from genomic DNA. Instead, an RNA template (a precursor mRNA) is constructed from the sequence of the gene. This RNA is then processed in various ways, including splicing. Spliced single-stranded RNAs destined to become templates for protein synthesis are known as mRNAs, The term mRNA is used only for a mature transcript with polyA tail and with all introns removed, rather than the primary transcript in the nucleus. As such, an mRNA will have a 5' untranslated region, a coding region, a 3' untranslated region and (almost always) a poly(A) tail. Typically about 2% of the total cellular RNA is mRNA.

mRNA Export:

Refers to the movement of spliced mRNA out of the nucleus to the cytoplasm.

mRNA Processing:

Refers to the processes of polyadenylation, splicing, and addition of a 5' cap structure.

Metaphase:

A stage in mitosis or meiosis during which the chromosomes are aligned along the equatorial plane of the cell.

Microsatellite:

A microsatellite is a simple sequence repeat (SSR). It might be a homopolymer ('...TTTTTTT...'), a dinucleotide repeat ('....CACACACACACACA.....'), trinucleotide repeat ('....AGTAGTAGTAGTAGT...') etc. Due to polymerase slip during DNA replication there is a slight chance these repeat sequences may become altered; copies of the repeat unit can be created or removed.

Missense Mutation:

A nucleotide mutation which results in a change in the amino acid sequence of the encoded protein.

Minor Groove Binders (MGBs):

These dsDNA-binding agents are attached to the 3’ end of TaqMan® probes to increase the Tm value (by stabilization of hybridization) and to design shorter probes. Longer probes reduce design flexibility and are less sensitive to mismatch discrimination. MGBs also reduce background fluorescence and increase dynamic range due to increased efficiency of reporter quenching.

Minus Reverse Transcriptase Control (_ RTC):

A quantitative real-time PCR control sample that contains the starting RNA and all other components for one-step reaction but no reverse transcriptase. Any amplification suggests genomic DNA contamination.

Mitosis:

The process of nuclear division in cells that produces daughter cells that are genetically identical to each other and to the parent cell.

Modified Bases:

These are those bases except the usual four from which DNA, RNA are synthesized, they result from postsynthetic changes in the nucleic acid.

Molecular Biology:

The biochemical study of the genetic basis for phenotype.

Molecular Beacon:

These hairpin probes consist of a sequence-specific loop region flanked by two inverted repeats. Reporter and quencher dyes are attached to each end of the molecule and remain in close contact unless sequence-specific binding occurs and reporter emission (FRET) occurs.

Molecular Chaperone:

It is a protein that is needed for the assembly or proper folding of some other protein, but which is not itself a component of the target complex.

Monocistronic:

A form of gene organization resulting in transcription of an mRNA that contains coding sequence for a single gene or gene product.

Monte Carlo effect:

Problems with reproducible quantification of low abundance targets (<1000 copies) by qPCR. It is a limitation of PCR amplification from small amounts of any complex template due to differences in amplification efficiency between individual templates in an amplifying cDNA population. The Monte Carlo effect is dependent upon template concentration; the lower the abundance of any template, the less likely its true abundance will be reflected in the amplified product.

Multiforked Chromosome:

It has more than one replication fork.

Multiplexing:

Simultaneous analysis of more than one target. Specific quantification of multiple targets that are amplified within a reaction can be performed using a differentially labeled primer or probes. Amplicon or probe melting curve analysis allows multiplexing in allelic discrimination if a dsDNA-binding dye is used as the detection chemistry.

Multimeric Proteins:

Proteins which consist of more than one subunit.