Читать книгу Essential Endocrinology and Diabetes - Richard I. G. Holt - Страница 98

Applying the principles of FISH on a genome‐wide scale in a microarray format is called ‘array comparative genomic hybridization’ (array CGH). Short stretches of the genome are printed as thousands of microscopic spots on a glass slide (the ‘microarray’). The patient’s genomic DNA is fluorescently labelled and hybridized to the spots on the slide. According to the strength of the fluorescent signal, microdeletions or duplications anywhere in the whole genome can be detected in one experiment with a resolution of several kilobases.

Single nucleotide polymorphism (SNP) arrays are being used similarly. Spread across the entire genome, there are millions of subtle variations (polymorphisms) at specific nucleotides between different individuals. On SNP arrays, the spots on the glass slide represent the different sequences at each SNP. As an individual’s paired chromosomes come one from each parent, this means that at any one SNP, there are often two different sequences (one from the mother, one from the father; this is called heterozygosity). Across stretches of DNA, SNP arrays can identify regions showing ‘loss of heterozygosity’ (i.e. there is no variation in the signal), which is indicative of deletion of either the maternal or paternal copy, or altered ratio of signals indicative of duplication.