Merle Genetics for Newcomers
This is and is intended to be a very basic explanation= of the workings of the merle gene. If you already know about blue merles and o= range merles, you may not find anything new here. If you're not sure why people g= et upset about orange merles and double merles, read and learn.
There is no such thing as an orange merle gene or blue merle gene. There= is only a merle gene. Merle is a dilution gene, that is, it lightens whatever = the coat color would otherwise have been. The lightening is not spread evenly o= ver the coat, but leaves patches of undiluted color scattered over the dog's bo= dy.
One dose of the merle gene = on an otherwise black dog produces a blue merle - a more or less bluish gray dog dappled with black spots. One dose of the merle gene on an otherwise orange= dog produces an orange merle. Orange merles are less predictable in color than = blue merles, and may range anywhere from an apparent sable, often with an orange cast to its coat, to very rusty. O= range merles are born dappled, but will not keep the spots in their adult coats.<= o:p>
Merle acts on the black pigment in the iris of the eye just as it does on the coat, so merle dogs often have part blue eyes, or one or both blue eyes. (This does not affect their vision, though since it happens to some extent = in the retina as well it may make it harder to diagnose certain eye problems.)=
The previous description was for a single dose of the merle gene. There = are always two copies of a gene, alike or different, in any dog. If we call the merle gene M and the non-merle gene m, any given dog can be mm, Mm or MM. T= he mm dog is the normal, full-colored coat. The Mm Sheltie is a blue merle or = orange merle, depending on what color it would have been without the merle gene. A= n MM dog, often called a double merle, will be mostly white and usually deaf or blind and often with other physical problems. Some MM puppies are born completely without eyes.
Breeding merle to full color will produce one half full color and one ha=
lf
merles, with no birth defects. The safe breeding for a merle, is to a non-m=
erle
mate. This breeding should produce all healthy puppies. The rule is that a
merle should be bred to a black, or black and white pa=
rti
only. You should not breed merles to orange, because this mating may produc=
e orange
merles. Orange merles are no more likely to have health problems than any o=
ther
color, and they are equally good companions. The real problem with orange merles is that they may be mistaken for
normal full color dogs because they don’t keep the merle spots. If
two such orange merles were mated together, the resulting litter could cont=
ain
defective pups. What a shock for the breeder expecting normal, healthy pupp=
ies!
The only safe breeding of merle to
orange would be to a DNA tested orange so you were sure that the merle gene=
is
not present.