method of separating large molecules (such as DNA
fragments or proteins) from a mixture of similar molecules. An electric
current is passed through a medium containing the mixture, and each kind
of molecule travels through the medium at a different rate, depending on
its electrical charge and size. Separation is based on these differences.
Agarose and acrylamide gels are the media commonly used for
electrophoresis of proteins and nucleic acids.
A technique that
separates DNA fragments on the basis or their size by running them through
a viscous material. The fragments move through the material due to the
application of an electric current which attracts the negatively charged
DNA to the positive terminal, and the fragments are separated due to the
fact that the smaller fragments will move through the matrix faster than
the larger fragments and will thus arrive sooner at the positive terminal.
Glossary of Forensic DNA terms
Elongation or extension
-Phase of PCR cycle following annealing of primer during
which the Taq polymerase synthesizes a strand of DNA. The optimum
temperature depends on the enzyme used but is usually between
Refers to the elongation of the DNA chain that is being
synthesized using the parent DNA strand as the template for synthesis of
that daughter strand. This is a natural process that occurs during DNA
replication. Extension occurs during the PCR process with DNA polymerases.
Ethidium Bromide ( EtBr )
Intercalates within the structure of nucleic acids in such a way
that they fluoresce under UV light. Ethidium bromide staining is commonly
used to visualize RNA or DNA in agarose gels placed on UV light boxes.
Proper precautions are required, because the ethidium bromide is highly
mutagenic and the UV light damaging to the eyes.
A Glossary of Terms commonly used in Molecular
Part of a gene whose sequence is present in a mature mRNA after splicing.
Expressed Sequence Tag
( EST )
A small sequence from an expressed gene that can be
amplified by PCR. ESTs act as physical markers for cloning and full length
sequencing of the cDNAs of expressed genes. Typically identified by
purifying mRNAs, converting to cDNAs, and then sequencing a portion of the
A partial sequence of a randomly chosen cDNA, obtained
from the results of a single DNA sequencing reaction. ESTs are used to
identify transcribed regions in genomic sequence, to characterize patterns
of gene expression in the tissue that was the source of the cDNA and as
markers for genetic mapping.