The Australian Shepherd comes in four basic body colors: Merle (Blue or Red), Solid (Black or Red) All with or without white and/or copper trim. A solid dog with white and copper trim is called a Tri Color. A solid dog with only white trim is called a Bi Color. A solid dog with only copper trim is called a black/red and copper. A merle with white and copper trim is called a "Merle". A merle with only white trim is called a "Merle with White". A merle with only copper trim is called a "Merle with Copper". For more information on Aussie colors, please read "The Merle Gene" by Pam Bethurum.
 | Gene - The basic unit of inheritance made up
of DNA which is responsible for the transmission of hereditary characteristics. |
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Dominant - A member of a gene pair that masks
the affect of the other member of the pair. The dominant member of the pair is usually expressed as a capital letter such as "B". |
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Recessive - A member of a gene pair that is
masked by the affect of the other member of the pair. The recessive member of a pair is usually expressed as a lower case letter, such as "b". |
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Homozygous - A gene pair which has the same
form of the gene on each chromosome. |
|
Heterozygous - A gene pair which has
different forms of the gene on each chromosome |
The basic body color of
the Aussie is controlled by the action of two separate gene pairs.
One gene pair controls the basic color of the dog, black or
red. This set of genes is usually referred to as B for black, which is the
dominant form of the gene; and b for red, which is the recessive form of
the gene. The black color is dominant over the red color. There are three
different combinations found in this gene pair:
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BB - This individual is
homozygous for the dominant trait. It only has the dominant black |
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Bb - This individual is
heterozygous for the dominant trait. It has both a black gene and a |
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bb - This individual is
homozygous for the recessive trait and is a red dog. This individual |
The other gene pair that affects the
basic body color of the Aussie is the merle gene. This gene pair is referred to
M for merle and m for solid. The merle gene acts upon the red or black color,
causing the spotting or merling. The merle color is dominant to the solid color.
Normal blue or red merle are
heterozygous for the merling gene. They carry one dominant merle gene and one
recessive solid gene (Mm). There are also three different combinations found in
this gene pair:
| MM - This individual is
homozygous for the dominant trait. It only has the dominant merle gene and is a merle white. A merle white is many times referred to as a "lethal white." A merle white can be a blue or a red merle with excessive white markings including some or all of the following: a half or full white head, white ears, a collar that extends past the point of the withers, white body splashes, or full white rear legs extending up the sides into the body color. A merle white can be anywhere from a dog with excessive white trim to the rare extreme of a solid white dog. This type of merle can ONLY be produced from the breeding together of two merles, producing a pup with two merle genes. A merle white is usually blind and/or deaf. Many times they will have two blue eyes and the pupils of the eyes will be misshapen, starburst in shape, or off center in the eye. The eyes many times will have multiple hereditary eye defects which is referred to as merle ocular dysgenesis (homozygous merle eye). They can be deaf due to the lack of pigment in the inner ear. There are also indications that these individuals may have other physical defects due to the action of the merle gene on the neural crest during embryonic development. The neural crest is an embryonic structure from which the nervous system, internal organs and eventually even pigment cells originate. The action of the merle gene is not totally understood at this time, but in its heterozygous state (a normal merle with one merle gene and one solid gene), the merle gene usually causes only the repression of the formation of pigment in the hair. In its homozygous (merle white) state, the individual has two merle genes, causing a more widespread effect on the developing embryo, including eye defects as well as possible internal defects. (The following discussions on this color is included for a better understanding of color genetics and NOT as a recommendation to breed merle whites.) This dog when bred to a normal heterozygous merle will produce homozygous merle whites (MM), and heterozygous merles (Mm). It will not produce solid color pups. |
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Mm - This individual is
heterozygous for the dominant trait. It has both a merle gene and a solid gene, but it is a merle dog because the merle gene is dominant and masks the affect of the solid gene. This dog when bred to a homozygous merle (MM) will produce homozygous merle whites (MM) and heterozygous merles (Mm). It will not produce solid color pups. This dog when bred to another heterozygous merle (Mm) will produce homozygous merles (MM), heterozygous merles (Mm) and solids (mm). This dog when bred to a solid will produce heterozygous merles (Mm) and solids (mm). |
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mm - This individual is
homozygous for the recessive trait and is a solid dog. This individual only has the recessive (m) gene to give to its offspring. It doesn't matter if both of its parents were merles. A solid colored dog does not have a merle gene (M) to give to its offspring. So, if it is bred to a homozygous merle (MM), it will only produce heterozygous merle (Mm) offspring. If it is bred to a heterozygous merle (Mm), it will produce heterozygous merles (Mm) and solids (mm). If it is bred to a solid, it will only produce solids (mm). |
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The Australian Shepherd Club of America (ASCA)