What's a gene chip? Well, it's not a gene chip, that's for sure. It's a microarray. It has various parts of a genome arrayed on a small chip. The parts of the genome you put on the chip depends on what you're interested in studying. You then take some DNA you're interested in and apply it to the chip. If a DNA sequence matches a sequence on the chip, it hybridizes to the part of the chip with the matching DNA sequencing. You then use a special technology to visualize which parts of the chip have DNA hybridized to them.
This technology can be used to differentiate between different single nucleotide polymorphisms (SNPs) across an entire genome. It can also be used to quantify transcripts of various genes in a genome based on how much hybridization occurs on the array. And it can be used to count the number of copies of a particular sequence in a genome; this is a way of quantifying copy number polymorphism.
Illumina is one of the leading makers of gene chips. They're in cahoots with both 23andMe and deCODEme. So, watch out, 'cause they're out to rule the world.
If you ignore butchering of the biology at the beginning, it's a pretty amusing video. Better watch out or they'll discover your genetic code, man.
(Via BBGM.)