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. Author manuscript; available in PMC: 2012 Mar 8.
Published in final edited form as: Equine Vet J. 2010 Oct;42(7):658–670. doi: 10.1111/j.2042-3306.2010.00166.x

Table 1.

Glossary of Terms

Term Definition
Genetics The study of genes and heredity; traditionally refers to classic Mendelian principles of inheritance.
Genomics The branch of genetics concerned with the global characterization of all of the genes and DNA sequence of organisms.
Polymorphism Genetic variation; usually refers to genes in which there are two or more alleles (slightly different forms of the same gene) circulating in a population.
Microsatellite Highly repetitive lengths of non-coding DNA involving multiple repeats of shorter segments of nucleotides (e.g. a di- tri-, or tetra-nucleotides). These genetic markers often display length polymorphism based on the number of repeat units. Determination of variation at microsatellite loci is widely used as a measure of polymorphism in a population and to identify near-by coding genes that determine traits of interest.
Pleiotropy The participation of a single gene in two or more unrelated processes; mutation of such genes therefore may produce seemingly unrelated effects in several organs, tissues, or cellular functions.
SNP Chip A single nucleotide polymorphism (SNP, pronounced snip) is a DNA sequence variation occurring when a single nucleotide – A, T, C, or G – in the genome differs between members of the same species. Mammalian genomes contain hundreds of thousands of SNPs dispersed widely throughout the genome. A SNP Chip is a miniaturized molecular device consisting of thousands of single stranded DNA oligonucleotide probes bonded to a silicon support. Each probe can be used to interrogate the DNA sequence at a single SNP locus using DNA hybridization. SNP Chips have become the method of choice for assessing variation across the genome; they are widely used in association and family studies designed to identify genes influencing traits of interest.
Expression Array The expression array is another type of multiplexed, miniaturized hybridization device. Expression arrays contain oligonucleotide probes for the expressed genes of an organism. Expression arrays are used to assess gene activation by providing a semi-quantitative estimate of the amount of mRNA encoding specific genes in a tissue sample, based upon hybridization of fluorescently labeled cDNA. Current equine expression arrays contain probes for nearly all of the estimated 20,000+ horse genes.