Well here you go ladies...this reading will answer all your comments.....
I have a lot more links because of my involvement with the Biewers and the pie-bald recessive gene. Here are just a few articles I have saved. The second article from London is the newest and even talks about the Biewers.
Practical Genetics
WHAT IS A RECESSIVE TRAIT? A recessive trait is a trait for which two copies of the gene must be present for the trait to be seen. This means that is takes two to tango & BOTH parents HAD TO HAVE the gene in question. This is VERY important to understand clearly, as complex dominance and polygenetic traits must be treated (somewhat) as one treats recessive traits to rid a bloodline of a problem or mimimize the effects of a trait. BOTH parents are PROVEN (obligate) CARRIERS if they EVER produce ONE SINGLE PUP EVER with a recessive trait. This means yellow (fawn,sable, red ) or blue/brown dogs out of black animals, yellow eyes from brown eyed animals, missing teeth, cataracts and hernias (in some breeds these are simple recessives), etc. There are many, many traits on this list. So don't point fingers & hide pups with recessive traits. Contact the stud owner, mark the pedigrees properly & help make progress in your breed (and your bloodline). Mark both parents as obligate carriers, mark all "normal" offspring as 66.66% likely to also be carriers & look for common relatives of the parents who likely brought the trait down to the current generation. Don't condemn--it takes two carriers to mate to find out you got a trait--consider this an opportunity to learn more about your bloodline.You don't have to toss all the dogs on the reject pile either necessarily. If the trait is acceptable (for all it is undesirable) & liveable for the dogs, then just letting it go may be an option. If the trait is serious, then how you treat it may depend on how widespread it is in your breed. If it is rare, then best to cull these animals who are carriers from the gene pool. If it is common, then such a drastic approach may not be reasonable & you will have to use carefully marked pedigrees and/or test breedings to control the expression of the gene. After all, remember, it is not the GENE that causes the problem, but the expression of that gene.
MITF and White Spotting in Dogs: A Population Study -- Schmutz et al. 100 (1): S66 -- Journal of Heredity
Pg 6 Table 2 Note under Yorkshire Terrier “Biewer”.
Genetics Of Coat Color In Dogs May Help Explain Human Stress And Weight Scientists Identify Genetic Basis For The Black Sheep Of The Family Wolf In Dog's Clothing? Black Wolves May Be First 'Genetically Modified' Predators Life As A Dog Means Faster Mutations Linkage and Segregation Analysis of Black and Brindle Coat Color in Domestic Dogs Selective sweep mapping of genes with large phenotypic effects