GENETIC TERMS

Gene - A unit of information on a chromosome

Allele - Two or more forms of the same gene (Example: Black or red)

Dominant - An allele is dominant if it produces its own effect and hides the presence of another allele. When a
dog has a copy of the black gene the dog is black in color. Black is dominant to red, so you can't tell by
looking if the dog has a copy of the red gene or not.

Recessive - An allele's effect is not seen if another, more dominant allele is present. Red is recessie to black.
For a dog to be red, he must have two copies of the red gene (bb). If he has a copy of red and one of black,
the effect of red will not be visible and the dog will be black (Bb).

Codominant - Neither allele dominates the other. If both are present, both are seen. The most common
example is the calico cat. Black and orange are codominant in cats. If both alleles are present, the cat has
both pigment colors.

Modifier - A gene that does not act on its own but exerts an effect on another gene. Modifying genes affect
how much copper is present in a tan pointed dog. If the dog doesn't have tan points (black bi, for example),
the effects of any modifiers of the tan point pattern will not be seen even though they're there.

Minus Modifier - A modifying gene or collection of modifying genes that acts to reduce pigment from whatever
color or pattern the dog already has. A solid colored dog, like a Lab or Doberman, with white on a toe or a
small collection of white hairs on the chest has minus modifiers pulling pigment from him even though he has
no spotting pattern. Minus modifiers can further reduce pigment on a dog with a spotting pattern to make a
collar extend beyond the withers.

Plus Modifier - A modifying gene or collection of modifying genes that adds pigment to whatever spotting
pattern is present. A full Irish spotting pattern (like Lassie's) can be reduced to white feet, a partial collar, and
little or no blaze, depending on their number and action.

Homozygous - "Homo" means "alike". A dog that is homozygous for an allele has two identical copies of it. A
red dog is homozygous for red (bb).

Heterozygous - "Hetero" means "different". A dog that is heterozygous for an allele has two different alleles for
that trait. A black dog that is heterozygous for black has one black allele and one red allele (Bb).

Polygenic Inheritance - A trait is caused by two or more genes working together. In Aussies, the natural bobtail
is polygenic. There are probably several muliple genes involved in determining exact iris color. The
inheritance of a trait dependent on multiple genes is harder to predict than one based on a simple
dominant/recessive relationship of alleles of the same gene.

© 2004 Lisa McDonald Feedback GENETIC TERMS

Gene - A unit of information on a chromosome

Allele - Two or more forms of the same gene (Example: Black or red)

Dominant - An allele is dominant if it produces its own effect and hides the presence of another allele. When a
dog has a copy of the black gene the dog is black in color. Black is dominant to red, so you can't tell by
looking if the dog has a copy of the red gene or not.

Recessive - An allele's effect is not seen if another, more dominant allele is present. Red is recessie to black.
For a dog to be red, he must have two copies of the red gene (bb). If he has a copy of red and one of black,
the effect of red will not be visible and the dog will be black (Bb).

Codominant - Neither allele dominates the other. If both are present, both are seen. The most common
example is the calico cat. Black and orange are codominant in cats. If both alleles are present, the cat has
both pigment colors.

Modifier - A gene that does not act on its own but exerts an effect on another gene. Modifying genes affect
how much copper is present in a tan pointed dog. If the dog doesn't have tan points (black bi, for example),
the effects of any modifiers of the tan point pattern will not be seen even though they're there.

Minus Modifier - A modifying gene or collection of modifying genes that acts to reduce pigment from whatever
color or pattern the dog already has. A solid colored dog, like a Lab or Doberman, with white on a toe or a
small collection of white hairs on the chest has minus modifiers pulling pigment from him even though he has
no spotting pattern. Minus modifiers can further reduce pigment on a dog with a spotting pattern to make a
collar extend beyond the withers.

Plus Modifier - A modifying gene or collection of modifying genes that adds pigment to whatever spotting
pattern is present. A full Irish spotting pattern (like Lassie's) can be reduced to white feet, a partial collar, and
little or no blaze, depending on their number and action.

Homozygous - "Homo" means "alike". A dog that is homozygous for an allele has two identical copies of it. A
red dog is homozygous for red (bb).

Heterozygous - "Hetero" means "different". A dog that is heterozygous for an allele has two different alleles for
that trait. A black dog that is heterozygous for black has one black allele and one red allele (Bb).

Polygenic Inheritance - A trait is caused by two or more genes working together. In Aussies, the natural bobtail
is polygenic. There are probably several muliple genes involved in determining exact iris color. The
inheritance of a trait dependent on multiple genes is harder to predict than one based on a simple
dominant/recessive relationship of alleles of the same gene.

© 2004 Lisa McDonald