Glossary of Terms

albino

An organism (especially a mammal) that is congenitally deficient in pigment and usually has a milky or translucent skin, white or colorless hair, and eyes with pink or blue iris and red pupil.

brindle

A dog coat color that is made up of a dark and a light color, in an alternating pattern resembling stripes. Not the same as merle^G.

coloboma

A congenital defect of the iris of the eye, it is visible as a hole, split, or cleft in the iris.

congenital

A condition present since birth. It can be genetic, or acquired during development in the uterus and not through heredity.

corectopia

Commonly called a "dropped" pupil, the pupil is not centered in the iris.

cryptic merle

A dog that is genotypically^G a merle, but phenotypically^G a solid. In other words, merles which have so little merling that they appear at first glance to be solids. There should be merle somewhere in their coat, even if it was only on their tail. They are still merles, and will produce merled offspring. To see pictures, go to Inheritance of Color in the Australian Shepherd - Cryptic Merles.

cysteine

And amino acid that is needed to produce pheomelanin^G.

dilution

A lighter shade of the original color. Merle^G is a dilution gene that only affects parts of the coat. Some merles can have "dilute spots," which are patches in their coat that are an off color (in blue merles, it is usually a muddy, brownish gray instead of clear black or blue - see Inheritance of Color in the Australian Shepherd - Dilute Spots for pictures). Other dilution genes affect the coat color evenly. It is possible for a dog to have more than one dilution factor at work (such as a black dog diluted to blue, but also having a merled coat and dilute spots - who could also be a homozygous merle).

dominant gene

A gene that produces the same phenotype^G, whether or not the other gene in the pair is identical. It will "cover up" the other gene. For example, a black dog only needs to be carrying one gene for black. Even if the other gene is red (brown), the black will override it. See also recessive^G gene.

double merle

A commonly used term to refer to a homozygous^G merle^G dog.

eccentric

This is a term used to describe a dog's eye where the pupil is misshapen.

eumelanin

A type of melanin^G that is made from tyrosine^G and causes brown to black pigment. The more tyrosinase^G activity, the more eumelanin is formed.

gene

The functional and physical unit of heredity passed from parent to offspring. Genes generally come in pairs.

genotype

The actual genetic constitution of an organism, regardless of outward appearance (see phenotype^G).

harlequin

A form of merle where it appears that the intermediate color is removed, leaving only the solid base color and white.

heterozygous

Having two genes at the same location that are different.

homozygous

Having two genes at the same location that are identical.

incomplete dominant

Merle^G is considered incompletely dominant because it doesn't behave the way that dominant genes typically do. Normally, a dominant gene completely covers the recessive half of the pair, so there is no difference in appearance between a dogs with one versus two copies of a dominant gene (in Aussies, black versus red is a good example). In merled dogs, those with one copy will have a normal merled coat, but those with two copies will have a mostly white coat. Because the "bad" effects of the merle gene only seem to show up in homozygous dogs, some people will refer to it is a recessive gene. This is not the case, because a recessive gene doesn't "show" in the heterozygous form. So even though merle doesn't completely cover the second gene, and in spite of the problems it can cause, it is still not a recessive.

Irish pattern/spotting

Typical "Lassie" collie markings - white blaze, collar, chest, and feet. In the series of genes for white, this is one with the least amount.

lethal

An abnormality of genetic origin causing the death of the organism possessing it.

lethal gene

A gene that in some (usually homozygous) conditions may prevent development or cause the death of an organism or its germ cells. A lethal gene is unsurvivable. Also called a lethal factor, lethal mutant, or lethal mutation.

mark/markings

A distinguishing trait or quality. A distinctive pattern or arrangement of color.

melanin

A form of protein that controls the pigment found in the skin, hair, and eyes of vertebrate animals. There are two major forms: eumelanin^G and pheomelanin^G

merle

An incompletely dominant^G dilution^G gene that lightens the base color in random, irregularly shaped areas.

microphthalmia

An abnormally small eye. Anophthalmia is complete absence of an eye.

mismark

Overextension of white trim or homozygous merle. Homozygous merles are merle in color and typically have much more white than is allowed in the Australian Shepherd standards. Overextension of white trim occurs anywhere outside of the Australian Shepherd standards (usually on the face/head, over the shoulders or withers and body splashes). Note: merle and white trim are determined by two different genes, please refer to "pattern white^G"

MM

An abbreviation designating a homozygous^G merle^G dog. Since merle is a dominant gene, it is signified with a capital M, and MM means that a dog carries 2 copies of the gene. MxM is used to designate a breeding of 2 merle dogs.

organism

Any living thing that has (or can develop) the ability to act or function independently.

pattern white

A dog with more white than is allowed by the breed standard. Can be either a merle or a solid.

phantom merle

please refer to "cryptic merle^G"

phenotype

The physical appearance/observable characteristics of an organism that are produced by the interaction of the genotype and the environment. (see also genotype^G)

pheomelanin

A type of melanin^G that is made from tyrosine^G and causes yellow to red pigment. It occurs when the amino acid cysteine^G interacts with the production ofeumelanin^G. The more interaction, the more yellow and orange pigments are produced.

piebald

A white genetic pattern, typically more than is seen on a dog with Irish spotting^G.

pigment

A substance that gives color to cells or tissues. Pigments are responsible for the color of skin, eyes, and hair.

recessive gene

A gene that will be expressed only when there are two identical copies (homozygous^G). For example, a dog can only be red (brown) when it carries both genes for red. If it has one black, it will be a black dog. See also dominant^G gene.

roan

In dogs, usually a white coat thickly sprinkled with a solid color. Sometimes the inverse (a solid color coat thickly sprinkled with white).

spotting

Color patterns produced by the interaction between white and solid color genes.

starburst pupil

This is a term used to describe a dog's eye where the pupil has spiky projections. Also called sunburst.

subluxated

This is a term used to describe a dog's eye where the pupil is not centered in the eye (correct term is "corectopia"). Usually it is lower or toward the inner corner. Also called dropped.

tapetum

An area in the pigmented layer of the choroid (which lies just behind the retina) of the eye in many animals, which has an iridescent or metallic luster and helps to make the eye visible in the dark. In most dog's it reflects a greenish color, but merled dogs will often have red eye shine.

ticking

Small spots visible in the coat/skin of a bird or mammal. Not visible at birth, but become more obvious as the dog matures.

tyrosinase

A copper-containing enzyme that affects melanin^G production and is widespread in animals.

tyrosine

An amino acid that is turned into either eumelanin^G or pheomelanin^G by tyrosinase^G.