Glossary of Genetic and Veterinary Terms


If you are unable to locate a term that you think would be a useful addition to this glossary or you find something you think needs to be corrected, please contact us.  Click on the first letter of the word you are looking for to go to that section.

A   B   C   D   E   F   G   H   I   J   K   L   M  N   O   P   Q   R   S   T   U   V  W   X   Y   Z


A – an abbreviation used by dog breeders for the gene agouti signal peptide (ASIP or Agouti); alleles of this gene may result in a dog that is sable, wolf grey, has tan points, or lacks them (“recessive black.”)

Additive Trait –  A trait regulated by a set of gene pairs, the sum of which determines the phenotype. These may be affected by environment (e.g. hip dysplasia.) They are quantitative traits (degree of dysplasia or joint laxity, amount of coat, depth of pigment, size of bone, etc.)

Agouti – a coat color gene, agouti signal peptide (abbr: ASIP or A) influencing the distribution of eumelanin and pheomelanin in the coat.

Affected –  An individual which has a hereditary disease.

Albino – 1.  An individual totally lacking in pigment – not known to exist in dogs, or 2. A gene determining intensity of pheomelanin.

Allele –  The form of a gene or other segment of DNA, such as a microsatellite. Example: There are two alleles for the merle gene, M (merle) and m (non-merle). Since genes come in pairs, any given individual will have only one or two types of allele for that gene or microsatellite. Some genes and all microsatellites have multiple alleles.

Allergy –  State of altered immune reactivity, resulting in reaction to foreign substances (food, airborne particles, etc.) that would not cause any reaction in a normal individual.

Anterior Cross-Bite –  Also called “wry mouth;” a condition in which one side of the jaw has grown longer than the other, causing a lop-sided malocclusion of the incisors and canines.

Artificial selection –  purposeful human-governed breeding of plants or animals.

Autoimmune Disease –  Diseases resulting from the immune system mistaking tissues as “other” rather than “self,” including thyroiditis, lupus, myasthenia gravis, and generalized demodectic mange. Tendency toward these diseases is often inherited and can be exacerbated by inbreeding.

Autosome –  Every chromosome except the sex chromosomes. 


B – abbreviation used by dog breeders for the gene tyrosinase related protein one (abbr: TYRP1) versions of which determine whether the dog is black or brown

BAER test – Brainstem Audio Evoked Response (BAER) is a test for deafness in dogs.  Earphones are placed over the dogs ears to play sounds and electrodes positioned on its head to measure electrical activity in the inner ear.  The responses are analyzed by a specialized computer.

Beta-defensin 103 – (abbr: CBN103 or K) a canine coat color gene differing versions of which produce tan coat color, lack fo tan in the coat, or the brindle pattern.

Bilateral – occurring on both sides of the body, e.g. both eyes, both ears, etc.

Brown – a coat color also variously referred to in dogs as liver, chocolate, or red.


C – abbreviation used by dog breeders for albino, a gene proposed to reduce the intensity of tan pigment in the coat.

Cancer – any of a large group of diseases typified by uncontrolled growth of abnormal cells.

Canine Multifocal Retinopathy (CMR) – blister-like retinal defects that may progress or go away.  CMR can be detected as early as four months of age and may be described as retinal dysplasia or retinal folds. Vision loss is possible, but rare.

Carrier – an individual that has a gene or genes for a particular trait but does not exhibit that trait or an individual with a single copy of a recessive mutation.

Cataract – an opacity (cloudy area) on the lens, a disc-shaped structure located behind the pupil which focuses vision.  Cataracts reduce vision and when advanced can be blinding.  They can be hereditary, caused by other diseases, or due to injury or nutritional abnormalities.

Choroidal hypoplasia (CH) – a thinning of the vascular tissue in the back of the eye present in both eyes of all CEA affected dogs.

Chorioretinal dysplasia – equivalent terminology for choroidal hypoplasia.  Commonly used in Europe.

Chromosome –  A gene-carrying structure in the nucleus of a cell. Chromosomes come in pairs and all species have a set number. In humans there are 46 chromosomes (23 pairs) and in dogs there are 78 (39 pairs.)

Clone – A genetic duplicate of the original individual. Clones can occur naturally; including “budding” in lower organisms and from multiple offspring developed from a single zygote (twins, etc.) in animals. Artificial clones can be produced via plant cuttings or genetic engineering.

Co-dominant –  a mode of inheritance in which both alleles in a heterozygote will express.  Example:  Human AB blood type, individuals with AB blood have an allele for Type A blood as well as one for Type B.

Coefficient of Inbreeding (COI) – A prediction of how likely a gene is to have two like versions which are identical by descent.  In other words, the dog will have inherited a particular gene version from the same ancestor down both sides of its pedigree, resulting in a homozygous (two like versions) gene pair.  The higher the COI, the more possibilities there are in a pedigree that this might happen, indicating the level of inbreeding in that pedigree.

Collie Eye Anomaly (CEA) –  a sometimes blinding eye disease;  all dogs with CEA have choroidal (or chorioretinal) hypoplasia, a thinning of the vascular tissue in the back of the eye.  This causes very little disruption of vision.  However, some dogs have optic nerve coloboma, incomplete development of the optic nerve where it enters the eye, or retinal detachment.  Either of these later conditions can be blinding.

Coloboma – failure of a portion of the eye to develop, e.g. iris coloboma, optic nerve coloboma

Complex trait – a trait with complex inheritance, thought to be due to some combination of genes, environment, and genetic regulatory factors.

Cone Degneration (CD) – a retinal disease causing day-blindness in puppies.  CD can be diatnosed by eight to twelve weeks of age.  There is a DNA test available.  The disease appears to have a recessive mode of inheritance, so both parents of an affected dog will be carriers.  Affected dogs should not be bred.  Carriers may be bred to clear-tested dogs.

Congenital –  present at birth; may or may not be hereditary.

Conserved DNA Sequence – a segment of DNA that has remained basically unchanged through evolution and therefore can be found in many species; generally felt to be involved in vital functions which are similar from species to species.

Corneal Dystrophy – opacity of the cornea; often hereditary.

Cross breeding – mating individuals from different breeds or distinct and separate populations.

Cryptorchidism – a hereditary condition in which one or both testes fail to descend into the scrotum. Unilateral cryptorchidism is often called “monorchidism,” which more properly refers to the complete absence of a testicle. 


D – an abbreviation used by dog breeders for the gene melanophilan (MLPH), versions of which result in dogs with either full or diluted black or liver color.

Demodectic Mange – also “demodicosis,” immune reaction to a mite (Demodex canis) which is a normal resident of the hair follicles of dogs.  Generalized demodectic mange, an extensive or chronic condition, is inherited.

Dilution – a reduction of black or liver coat color pigment due to having two copies of the recessive version of the gene melanocortin receptor 1 (MC1r or D); black dilutes are referred to variously as blue, maltese blue, or grey while liver dilutes may be called fawn, lilac, deadgrass, or isabella.  In dogs with coat patterns like brindle or merle, the areas that would have been black or liver (or lightened shades of eiher as in merles) will be significantly lighter than a dog that is not dilute.

Dilution Spots – discrete areas of diluted pigment in the coat.

Distichiasis–one or more abnormal eyelashes that grow toward the eye instead of away from it. Often these lashes are benign, but they sometimes cause painful abrasion to the cornea and may require surgical correction. They can occur at any age and may come and go. Mode of inheritance is not known.

Direct Gene Test – determines what specific alleles of a gene the individual has; the most accurate method of screening for hereditary disease.

DNA –  deoxyribonucleic acid; a long, double-helix shaped molecule that carries the genetic code and provides the blueprint for genetic inheritance.

DNA Fingerprinting –  the positive identification of an individual by matching specific DNA sequences, usually microsatellites, to a DNA sample known to have been collected from that individual.

Dominant – a mode of inheritance; a dominant allele’s acitivity will override that of recessive versions of the same gene. 

Double merle eye defects – see merle ocular dysgenesis

 Dropped Incisors – center lower incisors noticeably shorter than adjacent incisors, sometimes also slightly out of alignment with their neighbors. 


E – an abbreviation used by dog breeders for the gene melanocortin receptor 1 (MC1r) versions of which may produce a black or liver dog, the mask pattern, grizzle or domino in Salukis or Afghans respectively, or yellow.

Elbow dysplasia – any of several elbow defects:  fragmented medial coronoid process, ununited aconceal process or osteochondritis desicans of the elbow.

Epilepsy – a seizure disorder; the hereditary form of epilepsy is called primary or idiopathic.

Epistatic –  a gene whose action changes the phenotype expressed by another gene. Example: merle and brown (gene that determines b/ack/liver): Dogs will be either solid black or liver (also called red, chocolate, or brown) but if they have a dominant versin of the merle gene they will be merles, either red (liver) or blue merles depending on which versions of the brown gene the dog has.

Eumelanin – tan pigment in dogs

Exon –  a segment of DNA within a gene that contains instructions for making a protein.

Expressivity –  the variation of phenotype that occurs within a particular genotype. Example: Variations of merle patterning or spot shape and distribution on piebald animals. 


Founder –  an individual from whom at least some present-day members of a population descend and for whom no ancestral information is available. An “effective founder” is one whose ancestors are only represented through that individual.

Founder effect –  a form of genetic drift caused by a particular founder being more frequently an ancestor of members of the present population than are other founders, resulting in a higher frequency in the population of the alleles carried by that founder.

Fragmented medial coronoid process – (FCP) a separation of a bony prominence (process) of the ulna, one of the long bones below the elbow joint.

Frequency – of a gene:  percentage of a particular gene allele in a population. 


G – an abbreviation used by dog breeders for a gene for the dominant form of which causes coats to gradually turn grey, as in Kerry Blue Terriers

Gene –  a unit of inheritance; DNA sequences that provide the code for producing RNAs that build proteins or regulate gene function.

Gene therapy –  treatment of hereditary disease via the replacement of the defective gene with a healthy one.

Genetic –  of or pertaining to the genes; something which is genetic in origin may or may not be hereditary, e.g. acquired cancers

Genetic bottleneck –  restriction of a gene pool due to rapid and drastic reduction of population to a few individuals.

Genetic drift –  the tendency of specific alleles to vary in frequency from generation to generation. Rare alleles can be lost to a population by this process. Effects are more pronounced in smaller populations.

Genetic engineering –  the artificial manipulation of genes to alter function or insert them into a new organism.

Genetic fingerprinting –  using DNA markers to positively identify an individual

Genetic predisposition – a disease or condition highly influenced by environmental factors but which requires a certain combination of genes and regulatory DNA.

Genome – all the genetic material found in the chromosomes of a particular species

Genotype –  the genetic makeup of an individual.

Genotype – the specific combination of genes that give rise to a trait.  Example:  a black Aussie might have a genotype of BB (not a red carrier) or Bb (red carrier).

Germ cells –  reproductive cells; gametes; sperm and eggs.

Germ-line mutation –  mutations which arise in reproductive cells, inherited mutations.

Germinal reversion – spontaneous mutation of a gene allele to the wild type for that gene in a germ-line cell.

Glaucoma – a build-up of pressure within the eye due to blocked fluid ducts.  The pressure can damage the retina leading to blindness.  The disease is painful if not treated.  It is rare in Aussies and are not clearly established as inherited (it can be secondary to other things, including continued steroid use.)

Greying gene – a gene the dominant version of which can cause the coat to gradually turn grey starting in early adulthood. 


H – an abbreviation used by dog breeders for the gene proteasome subunit beta type 7 (PSMB7), which can produce the color pattern observed in Harlequin Great Danes if at least one copy of the dominant form of the merle gene is also present.

Haplotype – a combination of alleles located close together on a chromosome which tend to be inherited together.

Harlequin – a color pattern caused by the proteasome subunit beta 7 (PSMB7 or H) gene in Great Danes, sometimes mistakenly used to describe the tweed pattern in Australian Shepherds

Hemangiosarcoma – cancer of vascular tissue, equivalent to angiosarcoma in humans.  Tumore frequently arise in the spleen or liver, occasionally in blood vessels in the skin.  The cancer spreads readily to the lungs and other sites in the body.

Hemophilia –  either of two X-linked bleeding disorders, referred to as Hemophilia A and Hemophilia B. The latter is also known as “Christmas Disease.”

Hereditary traits –  traits passed from one generation to subsequent generations via DNA sequences inherited from one or both parents.

Heritability –  that portion of a trait which can be inherited (Example: Hip dysplasia is not 100% heritable because environmental conditions can affect its expression), also the degree of variation which can be influenced by heredity. (Example: All Schipperkes are black and black color is inherited, but the heritability of black in Schipperkes is 0% because they are all homozygous for the trait and there is no variation.)

Heterozygous-  having two different alleles for a particular gene.

Hip dysplasia – (HD) a degenerative disease of the hip joint associated with joint laxity.  HD is multifactorial and genetically predisposed.  Symptoms can range from subclinical to severe and generally worsen with age.

Homolog –   equivalent copies of a DNA structure, whether genes, chromosomes, or portions of chromosomes in different species.

Homologous Genes – genes that are the same or very similar in different species.

Homozygous –  having two like alleles for a particular gene.

Hyaloid artery –  an fetal structure within the eye; an artery which allows blood flow to the front of the developing eye then resolves (goes away) prior to birth.  Sometimes all or a portion of this structure may remain.

Hybrid vigor –  also heterosis; the superiority of the heterozygote over the homozygote for a specific trait; or the tendency of a first-generation cross between two distinct populations to be more productive or more fit than either of the parent strains.

Hypostatic –  condition in which a gene which can have its phenotype altered by action of another gene.  Example:  A dog which would otherwise be sable or have tan points due to the agouti gene will be black or liver in the presence of at least one dominant allele of the K gene.

 Hyperactive – an individual which will constantly be doing something; such dogs may become neurotic if unable to engage in a positive outlet for their energy.


Immune mediated – a disease or condition that is influenced to some degree by the inaction or abnormal action of the immune system.

Inbreeding – the breeding of related individuals.  This includes not only matings that in humans would be considered incestuous, but those that dog breeders term “linebreeding,” or between individuals that share ancestry beyond the typical printed pedigree.  All individuals in any species share ancestry; members of a pure breed will share even more and more recent ancestors than their species as a whole.  Inbreeding can become problematic when it is relatively recent and/or occurs at high levels (many connections on both sides of the pedigree.)

Incomplete dominant –  a mode of inheritance in which the heterozygote phenotype falls between the phenotypes of the homozygotes.  Example:  Roan in Shorthorn cattle (red is dominant and white recessive) or merle in dogs (multiple eye defects and variegated loss of pigment are dominant, no merle patterning is recessive.)

Intron – segments of DNA in a gene that do not code proteins.

iris Coloboma–a section of the iris which failed to develop. Almost all affected dogs are merle. A large coloboma will prevent the iris from dilating and contracting properly resulting in some discomfort and difficulty in bright light. 




K – abbreviation used by dog breeders for the gene beta-defensin 103 (CBN103); a gene that determines the brindle coat pattern and “dominant black,”  an absence of tan pigment areas. 


Lethal trait – a genetic trait that results in the early death of the organism. “Early” in this situation means before the organism would be likely to reproduce.

Linebreed – a breeding system in which emphasizes the appearance on both sides of the pedigree of related dogs, frequently one or more popular sires.

Linkage – genes or other DNA structures that are on the same chromosome, esp. when positioned close together. Linked DNA segments are usually inherited together; the closer the positioning the less likely they will be separated by recombination..

Locus – (pl. loci) the place on a chromosome where a particular gene or other DNA structure if found.

Lupus –  an autoimmune disease that may affect the skin or be or become systemic.


Luxation –  also sub-luxation; a partial dislocation of a joint or displacement of an ocular structure, such as the lens or pupil.

Lymphoma – cancer of the lymph tissue, found in two forms, B-cell and T-cell.  T-cell is the form most common in Australian Shepherds. 


M – an abbreviation used by dog breeders for the gene silver (SILV), the dominant version of which causes the variegated merle pattern on otherwise black or brown coats.

Major histocompatibility complex – (abbr: MHC) a group of genes that govern the function of the immune system; called a “complex” because they lie close together on the same chromosome and are usually inherited as a unit.  Lack of variation between MHC genes can impact proper immune system function.

Malocclusion –  failure of the upper and lower teeth or jaws to come together forming a proper bite, including overshot, undershot, wry and anterior crossbite.

Marker –  a segment of DNA, often a microsatellite, used for parentage verification purposes or as an indicator of the presence of a gene allele known to be close by on the chromosome.

Marker test – a type of DNA test used to determine the presence or absence of a marker, usually a microsatellite allele, known to be linked to  a gene version causing or highly associated with a particular disease or trait; marker tests can give false positive or false negative results should the marker become separated from the gene through recombination.

Megaesophagus – an abnormally enlarged esophagus.  Affected dogs cannot swallow or keep food or water normally.  It can be an inherited congenital condition.  However, it can also be secondary to other health problems.  Dogs with certain heart or neuromuscular diseases may develop megaesophagus.

Melanin – pigment produced by cells called melanocytes, there are two forms in dogs:  Eumelanin (black/brown) and pheomelanin (tan).

Melanocortin receptor 1 – (abbr: MC1r or E) a gene which determines distribution of eumelanin and pheomelanin in the coat in particular patterns, including all of one or the other or a the mask or grizzle/domino pattern.

Melanophilan – (abbr: MLPH or D) a gene which determines the amount of phaeomelanin, producing either full intensity of black or liver color or dilute (lighter) forms of those shades.


Mendelian – a trait which has relatively simple in inheritance; single-gene or qualitative

Merle – a variegated coat color pattern caused by the gene silver (SILV); homozygous dominant dogs are often mostly white, especially in breeds that normally have white markings; heterozygotes will have typical merle patterns, either black (blue) or liver; and homozygous recessive individuals are not merle patterned.

Merle ocular dysgenesis – a complex of often-blinding eye defects seen in dogs which inherit two copies of the merle gene.  Almost any eye tissue may be affected but most typically these dogs will have abnormally small eyes (microphthalmia), abnormal retinas and iris irregularities.  Eyes are typically without pigment (blue).

Microsatellites –  highly polymorphic repeating DNA sequences which lie between genes.

Microphthalmia –  abnormally small eye, often blind, most commonly seen in homozygous merles.

Mode of inheritance –  the manner in which a trait is genetically passed from one generation to the next (i.e. dominant, recessive, polygenic).

Muscular dystrophy –  a lethal neuromuscular disorder.

Mutant gene/allele – a version of a gene that is different from the version considered “normal” in a particular population or species; a gene version with the potential to produce a disease or other unwanted trait.

Mutation –  a change in the genetic code due to transcription errors or transpositions between chromosomes; misalignment of DNA sequences or loss or gain of chromosomes or portions thereof caused by radiation, toxic exposure or random error.

Myasthenia gravis –  an autoimmune disease in which the immune system attacks the myelin sheaths of muscular nerves. 


Natural selection –  successful (production of offspring which then produce) mating influenced only by non-human factors.

 Natural Bob Tail – (abbr. NBT) a tail which congenitally lacks the full complement of tail vertebrae.  The number of vertebrae absent can be highly variable.


Optic nerve coloboma – a failure of development, some portion of the optic nerve will be absent.  Usually associated with collie eye anomaly it is also seen in double merles.

Osteochondritis desicans – (abbr:  OCD) improperly developed cartilage within a joint which separates from the underlying tissue; it may form a lose flap or be free-floating.  OCD  may occur in any moving joint but in dogs is most typical in the shoulder or elbow.  When in the elbow it is usually associated with fragmented medial coronoid process.

Outcross – mating between individuals of different bloodlines or distinct populations; in dogs applies to mating largely unrelated individuals within a breed. 


Patellar luxation –  an hereditary joint disease featured by the tendency of the patella (kneecap) to slip out of place.

Patent ductus arteriosus – (abbr: PDA) Serious, sometimes fatal, heart defect; a fetal shunt which allows blood to bypass the lungs fails to resolve prior to birth, resulting in a heart murmur and poorly oxygenated blood.

Pelger-Huet Anomaly –   (abbr: PHA) a lethal incomplete dominant disorder. Heterozygotes are little affected but will exhibit abnormal white blood cells.

Penetrance – the frequency with which a dominant allele will express itself when paired with a different allele. Example: Bb dogs are always black, so the B allele is fully (or 100%) penetrant. If a quarter of such dogs were red, then the allele would have 75% penetrance.

Persistent pupilary membrane –  (abbr: PPM) the puiliary membrane is a fetal structure that covers the pupil before birth.  When parts of it fail to go away it is termed PPM.  PPM may be observed in young puppies but frequently is absent a few weeks or months later.  Sometimes, however, it will persist.  Most PPMs are attached only to the iris.  Some form sheets of tissue, or have one end attached to the lens or cornea.  Those with lens and corneal attachments may have blinding opacities of those tissues.

Phenotype – what can be observed or measured of an inherited trait.  Examples:  coat color or height at withers.

Pheomelanin – a form of pigment in dogs causing tan coloration on a portion of all of the coat.

Polygenic – a trait caused by multiple genes.

Polymorphic –  having many forms; a gene or other DNA locus with multiple alleles.

Popular sires – sometimes termed “matadors,” these are dogs known for great quality, stellar show or performance careers, and an ability to consistently produce quality offspring.  Overemphasis on particular popular sires in a line can increase the probability of producing whatever faults and diseases that particular dog happened to carry.  If a popular sire and his near kin become heavily used across the breed it will increase the level of inbreeding and consequent loss of genetic diversity within the breed population.

Porto-systemic shunt –  an fetal blood vessel which bypasses the liver; if it fails to dissolve, blood will not pass through the liver for filtering and cleaning, a potentially fatal condition.

Prevalence –  the frequency with which an inherited condition occurs in a population.

Progressive retinal atrophy – (PRA) any of several diseases characterized by the gradual degeneration of the retina.  When discussing PRA it is important to know which type is under discussion as they are caused by different genes and, in at least one case (Centralized PRA) is due to nutritional imbalance.

Progressive rod cone degeneration – (PRCD) the form of PRA most frequently encountered in Australian Shepherds.

Proteasome subunit beta type 7 – (abbr. PSMB7 or H) a gene that is a homozygous dominant lethal and in the heterozygote will cause absence of pigment in the harelequin pattern observed in Great Danes.




Rage syndrome –  a neurochemical brain disorder typified by sudden violent attacks on people, other animals or inanimate objects; these episodes are a form of seizure which occurs without any prior behavioral cue and of which the dog seem unaware after the incident.

Recessive –  mode of inheritance in which the allele which will not express unless it is homozygous.

Regulatory DNA – genes or other segments of DNA that control the function of other genes, switching them on and off or dialing their activity up or down

Retina – a thin layer of nerve tissue lining the inside of the back of the eye.

Retinal detachment – a condition in which the retina comes lose from the back of the eye.  It is potentially blinding and can be caused by head trauma and may also be associated with collie eye anomaly.

Retinal dysplasia –  congenital developmental defect of the retina; Cone Degeneration may be described as retinal dysplasia by an examiner.

Roan – a coat color pattern in which areas which would otherwise be white are heavily mixed with colored hair as seen in soe Australian Cattle Dogs and hounds, felt to be a variety of ticking. 


S – an abbreviation used by dog breeders for genes that cause white spotting patterns, there are actually at least two of these genes, one which causes the “mantle” pattern in Boxers, and the other causes the “irish” pattern seen in many collie-type breeds.

Selection –  the method by which matings occur, may be natural or artificial – by human determination.

Sex chromosomes –  chromosomes that determine gender of the individual. In mammals, females are XX and males are XY, therefore gender of offspring is determined by the male.

Sex-limited –  a trait which occurs only in one sex, though the genes for it may be carried by either. Example: Cryptorchidism.

Sex-linked – a trait that is caused by a gene on a sex chromosome, usually the X. (The Y contains very few genes, all of them related to specifically male traits.) X-linked disorders are passed from mother to son. In the rare instance that a female inherits two copies of such a gene (muscular dystrophy, for example) the effect is usually lethal. No Y-linked disorders have yet been identified, but if they exist they would pass from a father to all his sons.

Silver – (abbr: SILV) a gene that causes varegated black or brown pigment in the merle pattern.

Somatic cells –  all cells except germ cells.

Somatic mutation –  a mutation which occurs in a somatic cell. It will affect all cells descending from the mutant cell within the organism, but will not affect offspring. Cancer is usually the result of somatic mutation. 


T – an abbreviation used by dog breeders for a gene that causes ticking or roaning patterns in otherwise white areas of coat; absence of these patterns is recessive.

Tail lines –  direct male and female lines of descent in a pedigree, sometimes mistakenly assumed to be of more genetic importance than other lines of descent.

Threshold traits –  polygenic traits with limited phenotypes. When the combination of genes passes a “threshold,” the next phenotype will be achieved.

Thyroiditis –  autoimmune disease which attacks the thyroid gland leading to hypothyroidism.

Ticking – a dominant coat color pattern causing a greater or lesser number of spots in otherwise white areas of coat, these spots may be scattered and irregular, or – as in the Dalmatian – fairly regular in size and distribution.

Transposable element –  a segment of DNA that can translocate itself to another position in the genome.

Tweed – (abbr Tw)  a variegated color pattern in merle dogs producing several gradients of the base color of black or brown, sometimes mistakenly referred to in Australian Shepherds as harlequin.

Tyrosinase related protein 1 – (abbr: TYRP1 or B), a gene versions of which determine the amount of eumelanin in the hair, resulting in either black or brown (liver) color. 


Unilateral –  occurring only on one side of the body, e.g. deafness in only one ear

Ununited aconceal process – (UAP) complete or partial detachment of a prominence (process) at the upper end of the ulna at the elbow joint. 


VonWillebrand’s Disease –  a clotting disorder that may be due to a recessive gene mutation or secondary to thyroid disease.


Wild type – the version of a gene felt to be typical or evolutionarily ancestral in the population or species under consideration.

 Wry bite –  deformation of the lower jaw in which one side is longer than the other, resulting in a “crossing over” effect between the upper and lower incisors; also called “wry mouth.” 




Zygote –  in animals, fertilized egg; zygotes develop into embryos, clusters of undifferentiated cells.  As cells begin to differentiate the embryo becomes a fetus.