Genetics of Miniature Schnauzer
Miniature Schnauzer and other races have half of their chromosomes inherited from the sire and the other half of your dam organized in pairs. Each chromosome consists of a DNA molecule that may have genetic information (genes) for different phenotypes (characteristics). In recent years, different genes have been identified through studies in molecular genetics, although the basic concepts of inheritance have been postulated by Gregor Mendel in the nineteenth century.
Places where the genes are present in the chromosomes are gene loci and in each homologous chromosome there are a copy of the gene. Each locus, will have one allele from the mother and one from the father called gene alleles. The information contained in these genes can be expressed with different intensity and therefore may be an allele is expressed more than the other. Thus, alleles may present themselves as dominant or recessive.
An example, a particular gene found A may appear in two locus in dominant form AA (homozygous dominant), a locus dominant and recessive in the other Aa (heterozygous) or two recessive locus as aa (homozygous recessive). The expression of the dominant gene in many instances prevents the expression of the recessive gene, but this is not a rule. During the evolution permanent changes may occur in DNA (mutations), causing a change in allele of the gene, that is, through a dominant gene to be recessive or vice versa.
Mutations can lead to loss of function of a gene or a new function and, consequently, lead to the formation of a protein variant is likely to have distinct properties as a result of its structure changed. Contrary to what many people think, the mutations do not always adversely alter the genetic information (genes). They can be either beneficial, neutral or deleterious. In the case of coat color Schnauzer, the appearance of white may be due to a beneficial mutation of the type generating the recessive gene and subsequently generated a different color in the race.
On the other hand, diseases that may appear in the race as kidney problems, vision, cancer and others, may be the result of deleterious mutations. Therefore, some crosses may generate the appearance of undesirable characteristics and are typically defined by homozygous recessive gene. When we seek a trait important in making the crossing between close dogs have to be very careful because it increases the chance of being with two heterozygous and therefore generate a homozygous recessive trait to provide a significant deleterious immediately or over the life of the animal.
There are four common forms of inbreeding: Inbreeding, crossing between close dogs such as parents and children, siblings etc. Line Breeding, crossing dogs with many common ancestors as grandparents and grandchildren, uncles with nephews etc. Outcrossing crossing between dogs that are products from a Line Breeding, but of two different blood lines and Outbreeding, crossing dogs unrelated.
In dogs, there are proposals of the existence of 12 genes involved in color, A, B, C, D, E, G, M, R, S, T and K. Not all of these genes are present in different breeds. In the Schnauzer D gene responsible for the dilution of two basic types of melanin in mammals, eumelanin and pheomelanin, is demonstrably absent. On the other hand, studies developed by the genetics laboratory HealthGene Canada, show that only two alleles are directly related to coat color Schnauzer, genes K and E. The gene E has direct interaction with the K in the form of epistasis, in this case the gene E inhibits (epistatic gene) the action of your alleles K (hypostatic gene), but only when it is the double recessive, called recessive epistasis. So, when the alleles E are homozygous dominant (EE) or heterozygous (Ee) is not inhibiting the action of the K gene, in these cases there is no epistasis. Assuming an inheritance based on the presence of only two genes (E and K) and the occurrence of epistasis, we have the following genotypes and phenotypes shown in Table 1.
TABLE 1 - Genotypes for coat color in Miniature Schnauzer
We can observe that, according to Table 1, the colors Salt and Pepper and Black and Silver have the same genotype and in this case, there must be some other gene that is related to the degree and distribution of pigmentation of these two varieties that have not yet discovered.
The crossing between dogs of different genotypes may result in different phenotypes. For example, a cross between a stud and matrix with the genotype KK EE can only produce puppies with the genotype KK EE. Table 2 shows other results of crosses. In the second case, Kk EE, the gametes of both sire and dam may present two different combinations: KE and kE by self-segregation during meiosis to formation of sperm and egg cells (Fig. 1).
Figure 1 - Meiosis with independent segregation and possible phenotypes and genotypes of the puppies.
When the sperm cell and an egg cell get together, the embryo will present the genotype for coat color with 75% chance of being black and 25% of salt and pepper or black and silver (Fig. 2)
Figure 2 - Punnett square with the crossings and the probability of possible genotypes and phenotypes of puppies.
Table 2 - Possible phenotypes from crosses between different genotypes.
