I'm coming in this discussion a bit late but to the OP, hopefully this explanation can help you understand where the off colors come from - these colors are all in the genes (or lack of genes). I'll try to make it simple, so you can get an idea on how color genetics and recessive genes work.
The majority of our yorkies are black and tan in color with at least one copy of the grey gene, which dilutes their black coat coloring to blue as the pup grows. Each parent has either no copies of the grey gene and have black coats, or they have 1 copy of the grey gene and have blue coats (heterozygous for grey and will pass that gene on to 50% of it's offspring) or 2 copies of the grey gene and have blue coats. Dog who have two copies of the grey gene, received 1 grey gene from their mother and 1 grey gene from their father. These dogs are homozygous for grey and will pass that grey gene on to 100% of their offspring.
A number of our traditional colored yorkies have recessive (hidden) genes for color too, that's where the parti, golden and chocolate colors come in. In order for this hidden recessive gene to make an appearance, two dogs who carry this gene, are bred together. The resulting litter will consist of 25% of the pups being traditional colored who did not get a copy of the recessive color gene, 50% of the pups will look traditional colored and do receive 1 copy of the recessive color gene and 25% of the pups receive 2 copies of the recessive color gene and display the off coloring (parti, golden, or chocolate). A golden, chocolate or parti colored yorkie will pass 1 of it's colorful genes to all of it's offspring because they are homozygous for their color (they have 2 copies of the gene and have to pass one copy onto it's offspring). Even if a pup is born that looks like a traditional colored yorkie, it carries 1 copy of that colorful gene and that carrier pup will then go on to pass the gene onto 1/2 of his own offspring.
These recessive colorful genes have been in the breed since it's beginning. It's documented in early American Kennel Club Stud books that in addition to yorkies being born blue and tan and black and tan, there were also other colors listed like "Tan," "Dark Tan" and "Blue" being noted. Some of our first US born show yorkies were born completely blue in color (not blue and tan), even Ernest Hemmingway's grandfather owned a white yorkie in the early 1900's.
Off color has popped up in the litters of some very well known and highly regarded old time breeders during the early to mid 1900's. But back in the old days, it was thought that the off color was a genetic defect or freak of nature, we are now wiser and have a better understanding of how recessive genes can hide for generations and appear when the right breeding takes place (a breeding where both parents carry the same recessive color gene).
Chocolate, golden and parti colored dogs are no more prone to health problems than traditional colored yorkies are, though parti coloring in some animals, do have hearing problems. We have yet to discover any deafness issues with the parti colored yorkies. |