The Color of the Labrador Retriever
Genetics analyzes the results of the interaction of a group of genes that lead to a variety of results: that dogs have the head long or short, strong or weak legs,fat tail or mouse tail depends on the combination of genes of the father and mother.
Each cell-dog or any other animal’s cell, contains a nucleus that is a "ribbon" called chromosomes. The number of these is constant in each species, and dogs have 78. The chromosomes are arranged in pairs, and each chromosome of each pair comes from one parent.
Sex cells have only 39 chromosomes, so that during the concrete conception the chromosomes will join in a normal cell with 78 chromosomes that will form the cub conceived. Sex cells are, therefore, the only exception to the number of 78 chromosomes in the dog.
The fact that the sex cells of the father and mother come together to form the puppy's genetic indicates that, contrary to some "folk" terms, genes affect offspring equally regardless of whether they come from the mother or father.
The chromosome is composed of genes, probably thousands of them, you
should understand that the gene is the hereditary unit that contains a specific statements about some features of the animal, this instruction does not change but it is repeated from generation to generation.
Each gene is found in a specific location within a specific chromosome, and that location is called the locus, Latin expression that means a place (plural loci).
As each gene is at a specific locus in a chromosome and if there are two identical chromosomes in each dog, it means that there are two genes at this locus (one on each chromosome), which are somehow "competing" for determining a characteristic of dog. These two genes are called alleles.
There are dominant and recessive alleles. Mastering this "competition" means that if a particular allele is present, it is enough to determine the characteristic of the dog. The recession, however, does not make for themselves, but when the other allele is also recessive, and come together to identify the feature.
The color of the Labrador:
There are many features of the dog that are determined by a variety of genes, whose analysis is extremely complex. The coat color of the Labrador is, however, one of the simplest cases. This is so for two things. The first is that in the black and yellow dogs there is a simple genetic dominance: the black dominates yellow.
In other words, the situation is simple because there is a gene whose presence determines the appearance, dominating the other. Hence the name of the chromosomes: In one case we are talking about dominant and recessive in the other. The recessive is not manifest in this generation but remains, and is constantly transmitted to subsequent generations, waiting to appear later. The issue of inheritance of chocolate coat is just slightly less simple, as it will be discussed below.
It is worth mentioning here the difference between genotype, the genetic constitution of the animal, and its phenotype, or outward appearance. In the case of single domain, if the genotype contains uun dominant gene will show the phenotype.
The second reason for the simplicity of the inheritance of coat color in Labradors is that in dogs ,in general, there are three genes that affect coat color: Ah locus, the locus B1, and locus E.
The simplicity referred to above is that the Labrador in the locus AY does not play any role - if so, we would see a lot of things (like spotted dogs as Dalmatians, with two colors such as German Shepherds, etc.) and we do not see in crosses of Labradors. Therefore, in this breed only Bb and Ee loci determine the coat and the other pigments: rimmel in the eyes, the color of the nose and gums, and the pads of the feet,along with shades of fur.
The E locus determines the existence of dark pigment, so that each gene and (recessive) implies that a parent does not provide dark pigment. From its part, the B locus determines that dark pigment color is black if at least there is one dominant gene B, or if it is oxidized to a brown color when there are two recessive b. Thus,a table can be built of all possible combinations. This was convenient to invent names for the different combinations of genotypes within a given phenotype.
The different colors of labrador:
Thus, Black Labradors (black phenotype) are divided into N1, N2, N3 and N4 as are their loci Bb and Ee are. This reflects that there are four black phenotype genotypes: N1 to call those bbee, N2 to bbee, N3 to N4 with bbee and those with bbee. What defines a black phenotype is that they have at least one E (a dark pigment) and at least a B (it does not rust).
There are two types of chocolate lab , the C1 and C2. All chocolate dogs, by definition, are bb for the dark rust, however that not all bb is chocolate.C1 or C2 will be depending on whether the dogs have EE or Ee respectively.
Finally, there are three types of yellow, A1, A2 and A3, as they mayso by having Bbee genotype, or bbee Bbee, what defines the yellow is the ee, the absence of dark pigment.
Note that the presence of recessive alleles ee determined there is no dark pigment in the coat, ie ee has no effect on the color of other parts of the dog as the nose or eye rims. In contrast, the other allele recessive, bb, oxidizes the pigment around the dog, so it also decreases the pigmentation of the nose and footpads, and the nose is lighter, even pink. So there are yellow dogs with dark noses and rimmel, called A1 (Bbee) and A2 (Bbee), and yellow dogs with nose and eye rims of even lighter pink with bbee are called the A3, also, these dogs tend to have light eyes.
From what was said above there are two initial comments: first, from crosses between yellow,the resulta are yellows of many types (the standardized name "yellow" goes from the "red fox" to "light cream") but do not go by any chance , chocolate or black. This is the fundamental characteristic of recessive colors: if the phenotype of both dogs to be crossed corresponds to the recessive color, none of the two genotypes of the parents have dominant genes (which, if any, it would have manifested itself) and therefore this gene cannot occur in the puppies.
Second, there are several possible types of Labrador dogs coming from the crossing of yellow and chocolate parents. All the books say that this cross should not be done: and I agree with that in spite of the fact that the risk referred to in books - poorly pigmented dogs - is given, but not always. This is probably due to the following: The specimen is always chocolate bb. Meanwhile, if the specimen is A1 which brings BB yellow, and all puppies will be Bb - which is not listed with the bb allele that leads to low pigmentation. If the yellow dogs is A2, it is Bb, so that half of the puppies will be bb. Finally, if the yellow copy is A3, all puppies will be bb. The probability of low pigmentation, then, is of 50% if we do not know, a priori, the genotype of yellow sample.
Consider the children of yellow puppies crossed with chocolate, when in both cases it is unknown the genotypes of the parents. First, 37.5 percent of the pups will be black (the breeder's little surprise), the same amount will be chocolate and 25 percent will be yellow.
Of the yellow puppies, half are A2, with some risk of lack of pigmentation, the other half are A3, with greater risk of poor pigmentation. Well pigmented, not even by chance.
So if you know the genotype of both parents and you cross with yellow with chocolate:
- All chocolates have bad pigmentation risk because they will be C2, and
- The yellows have 50% chance of being somewhat despigmented (A2) and 50% chance of being very despigmented (A3).
Furthermore, when that risk is not concentrated in the first generation, it is likely to concrete in at least some of the second generation puppies unless the dog with risk of despigmentation is crossed with a black one, ideally a pure black.
Hence, I think, that the books say that you should avoid crossing yellow and chocolate that can be crossed with chocolate chocolate provided the black one again, each time, to reinforce pigment.