A DNA microarray (also commonly known as gene chip, DNA chip, or biochip) is a collection of microscopic DNA spots attached to a solid surface, such as glass, plastic or silicon chip forming an array for the purpose of expression profiling, monitoring expression levels for thousands of genes simultaneously.

In oligonucleotide microarrays (or single-channel microarrays), the probes are designed to match parts of the sequence of known or predicted mRNAs. These microarrays give estimations of the absolute value of gene expression and therefore the comparison of two conditions requires the use of two separate microarrays.¹

Zebrafish DNA microarray screen results

http://www-micro.msb.le.ac.uk/3035/3035Immunopath.html

RNA interference (RNAi) is a technique used in molecular biology where fragments of double-stranded RNA (dsRNA) are used to intefere with the expression of a target gene which shares homologous regions with the dsRNA.

RNAi has recently been applied as an experimental technique to "knockdown" genes in model organisms for experimental analysis in determining the function of a gene. Repressing a gene from being expressed allows for testing of the protein and its role in the life of a cell or larger organism. Since RNAi may not totally abolish expression of a gene, using it against a gene is sometimes referred as a "knockdown", to distinguish it from procedures in which the DNA sequence encoding a gene is removed.²

Drosophila RNAi screen results.