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Glossary of Genetic Terms

Addison’s Disease (Hypoadrenocorticism)
A deficient secretion of both glucocorticoids and mineralcorticoids from the adrenal cortex. The cause is unknown, but in most cases, there appears to be an immune mediated destruction of the adrenal gland.  Symptoms include inappetance, vomiting, lethargy and weakness. An ACTH stimulation test can be used for diagnosis. The test is an evaluation of the ability of the adrenal gland to secrete cortisol.  Affected dogs show low cortisol concentrations, and no increase in cortisol following the ACTH test. Treatment includes fluid therapy, replacement of glucocorticoids and mineralcorticoids, and hormone therapy.

Phenotypic trait or gene NOT associated with either the X or Y sex chromosome; i.e., not sex-linked.

Existing at or before birth resulting from hereditary or environmental influences.

A condition involving recurrent seizures, which are convulsions caused by abnormal bursts of electrical activity in the brain. Seizures may last from seconds to minutes, and may include jerking of the limbs, anxiety, salivating, vocalizing, and loss of bodily functions (urinating/defecating).   Epilepsy can be caused by metabolic disorders, infectious diseases, brain injury, toxins, or brain tumors. In dogs, idiopathic (or inherited) epilepsy refers to a genetic seizure condition of unknown cause. Since a dog with idiopathic epilepsy shows no recognizable abnormalities, it is assumed to be an inherited condition in most breeds and has been demonstrated to be heritable in some breeds.  Treatment of seizures is usually two-fold which includes treatment of the underlying problem (infection, tumor, injury) and reducing or eliminating the seizure episodes with anticonvulsant medication.

Complete set of chromosomes carried in a cell.

Genome-Wide Association Study (GWAS)
A genetic examination using SNPs to see if a genetic variant associated with a specific trait exists among different individuals.  A comparison of DNA from two different groups, for example, dogs with the disease (cases) and dogs without the disease (controls).

Gibbs sampling
Method of calculating the genetic merit of dogs that takes advantage of fast computers. The process itself is just a computer-based method for integrating a function without having to find the antiderivative.

Arising spontaneously with no obvious external cause (e.g., genetic as opposed to trauma-induced).

Locus (plural – loci)
Site or position on a chromosome where a particular gene or DNA sequence resides. Often used interchangeably with the term ‘gene’, but locus is more generic.

As used here, a region of the DNA that can be consistently identified, using a laboratory procedure, across all individuals in a single breed. Microsatellites themselves are repetitive DNA sequences that are randomly distributed throughout the mammalian genome, tend to be highly polymorphic, and are short DNA segments.

The observable characteristics or traits of an individual.

Phenotypic trait whose expression is controlled by, or associated with, more than one gene.

Presence of several common, alternate forms of a genetic characteristic in a population.

Trait that requires two mutant copies of the gene (i.e., alleles) in order for the disorder to be expressed; must be homozygous for the mutant allele.

Single nucleotide polymorphisms, pronounced “snips”, are DNA sequence variations that occur when a single nucleotide (A,T,C,or G) in the genome sequence is altered.

Symmetrical Lupoid Onychodystrophy (SLO)
SLO is a disorder in Bearded Collies, as well as other breeds, that causes loss of toenails. The age of onset is typically between 3-8 years of age affecting 1-2 nails and eventually progressing to all nails. SLO requires lifelong fatty acid supplementation.

A distinguishing quality or characteristic of an individual, such as hair color or eye color.

Whole Genome Sequencing (WGS)
WGS is the process of determining the complete DNA sequence (genome) of the dog at one time. The dog genome contains 38 autosomal chromosomes with approximately 2.5 billion DNA base pairs with over 6 million variants (SNPs). A comparison of genome sequences from cases and controls can be used to identify causative variants associated with disease. WGS generates large amounts of data making the analysis process very tedious.