Genotyping
Genotyping is the process of determining the genetic constitution – the genotype – of an individual by examining their DNA sequence. Genotyping can be applied to a broad range of organisms, including microorganisms. For example, viruses and bacteria can be genotyped. Humans can also be genotyped.

DNA is isolated from a saliva or blood sample; it is then copied several times through a process called PCR, or polymerase chain reaction. Once a large quantity of DNA has been made, it is cut up into millions of short pieces. The millions of short DNA pieces are then labeled and loaded into a microarray for genotyping analysis. The microarray is placed in a rotating incubator for 16 to 18 hours; the mixing and heat from the incubator helps the short, labeled DNA pieces bind to the DNA fragments, or probes, which are attached to the surface of the microarray, like two sides of a zipper coming together. After washing away unbound DNA, a fluorescent stain is added to the microarray. This stain attaches to the labeled DNA and creates a visible light signal at spots in the person’s genome where there is a variation in their genome sequence. A laser is used to read the signals and a computer translates this information into a person’s individual genome profile.

Expression Profiling
In genetics, gene expression is the most fundamental level at which the genotype (the genetic makeup of a cell, an organism, or an individual) gives rise to the phenotype (any observable characteristic of a gene).

Every cell in the body contains a full set of chromosomes and identical genes, with a few exceptions. However, only a fraction of these genes are turned on – or “expressed” – and it is this subset of genes that confers the unique properties of each cell type. This biological mechanism acts as both an "on/off" switch to control which genes are expressed within a cell, as well as a "volume control" that increases or decreases the level of expression of particular genes.

Disruptions or changes at any step of gene expression are responsible for many genetic diseases. Through the use of microarrays, scientists can determine – in a single experiment – the expression levels of hundreds or thousands of genes within a cell.