Živjo,
na današnjem vzrejnem pregledu je tekel pogovor o rumenih starših in črnih potomcih (na temle forumu je bilo o tem že pred časom nekaj napisanega). Spodaj je skopiran del besedila in link na dobrih 10 let star prispevek - morda se najde tudi kaj mlajšega?
http://www.labbies.com/genetics2.htmBlack Puppies Produced from Two Yellow Parents?...Or From Two Chocolate Parents?..."Impossible!" You Say?...Maybe Not!... Geneticists recognize that there are two gene loci that are capable of controlling production of the yellow color in the dog. In Labradors, homozygous "e" at the Extension loci is considered the predominant genotype for producing yellow. However, in some other breeds, homozygous "ay" at the Agouti loci is recognized as being responsible for producing the yellow (tan/sable) color in dogs with the wild-type (E+) Mc1r, such as in the Basenji, Collie, Dachshund, etc.
The yellow (buff) color of the Cocker Spaniel was once believed only to be determined by homozygous "e" just as in the Labrador. Interestingly, however, upon occasion when two yellow Cocker Spaniels are bred, a black puppy will be produced. This observation was first made by Clarence Little in 1957 and later confirmed by Burns and Fraser in 1966. Because these test breedings were controlled studies, the possibility of mismating as an explanation was ruled out and a new hypothesis was postulated: There are two kinds of "yellow" Cocker Spaniels, an AsAsB_ee Cocker Spaniel that is usually buff-colored and an ayayB_E+E+ Cocker Spaniel that is usually sable-colored. When these genotypes are crossed, one possible resulting genotype of the offspring will be AsayB_E+e: a black Cocker Spaniel!
This scenario may not be limited to the Cocker Spaniel breed. Occasionally, black puppies are produced from yellow Lab X yellow Lab crosses. Some Lab breeders immediately cry "mismating", however, mismating is clearly not the only explanation since many times mismating is ruled-out by virtue of circumstance (ie. the bitch was exposed only to the intended stud and there was no opportunity for breeding to occur with any other male). In addition to what has been observed for the Cocker Spaniel, there may be additional indications supporting this theory. One author has suggested that the way to distinguish between a homozygous "e" yellow and a homozygous "ay" yellow is to examine the whiskers: If the whiskers are cream or straw colored the dog is homozygous "e", if the whiskers are black then the dog is homozygous "ay" (refer to: "Canine Color Genetics" by Sue Ann Bowling).
It is possible that like the Cocker Spaniel breed, the Labrador has two genotypic "kinds" of yellow dog: one that is homozygous "e" (more common) and one that is homozygous "ay" (less common) with the wild-type Mc1r (E+). As such, crossing these two different genotypic types of yellow Lab could produce an occasional black puppy from two yellow parents. This may also explain why occasionally a black puppy is whelped in litters from a chocolate to chocolate cross. It is also conceivable that some of these ayay Labs, especially if they are homozygous "C" at the C locus may appear to be chocolates rather than yellows (albeit with a more red-tone than a brown tone). As such, crossing of one of these chocolate-appearing yellow Labs with a true chococlate would produce AsayBbEE+: a black Lab.
Copyright © 1999. Pamela A. Davol.
The copy made for educational purposes
