This Genetics article is not meant to be a genetics book or a complete guide to the genetics of the Savannah cat. Rather it is a beginning resource for breeders or those who wish to become responsible breeders and who should know some of the basics before making the decision to begin on the breeding path. Inheritance and the effect of inheritance are very important aspects that a person should know before buying the queen and stud.
Homologous Chromosome is a set. When referring to offspring, as in kittens, one chromosome comes from the mother and one from the father. These chromosomes align correctly at the same point on the chain from both parents when the parents are the same species. While forming the offspring, the chromosomes combine and very simply, form new and different mixes of the two parents. Domestic cats and servals alike have 38 chromosomes or 19 pairs.
Each individual position on the chromosome is an allele.
Locus is the exact number location/position on the chain of 38 chromosomes, such as number 14 or number 3.
Diploid is an animal, humans included, which has a two position chromosome. There are mammals that have a four position chromosome but they are rare and not found in cats.
Zygosity is the degree of likeness (homozygous) or difference (heterozygous) of the alleles on any given chromosome.
Homozygous occurs when both alleles received the same gene passed on from both parents and can be either a dominant or recessive trait. As in pattern for instance. If both parents are spotted and carry for the classic (marbled) pattern and they both happen to pass on this recessive pattern, the two spotted parents can have a homozygous classic patterned kitten
This also means the parents are not Homozygous for the spotted pattern. Taking this a step further a spotted patterned cat can be bred to a classic patterned cat and all the kittens can be spotted. This may be a clue that the spotted cat may be homozygous for spotting. Repeating the breeding a few more times and only spotted kittens occur and we then know positively the spotted parent is homozygous for spotting because it takes two classic genes to make a classic pattern and the homozygous cat cannot pass on classic.
Heterozygous is simply when the allele passed on from the mother is different than the allele passed on by the father and if one parent passes on a dominant gene the offspring will exhibit that dominant gene as well. The trait on the other allele is going to be carried only and not exhibited. It is impossible for the recessive to be exhibited unless it is homozygous.
This holds true in the case of a spotted cat that carries for classic patterning. If you breed that spotted to another spotted who carries classic and you can have classic patterned kittens because both parents could pass on the recessive gene. This is a very simplistic explanation but can get very complicated depending on the complexity of dominance in genes.
OR Both Different
Dominant genes actually refer back to the inheritance of chromosomes from parents. As stated earlier, one gene from the mother and one from the father. One of the two alleles of each gene is dominant over the other.
Recessive, with dominant in mind, recessive is the other half of the equation. It can be passed either from mother or father and will take a back seat to the dominant gene. This is true on every gene except the sex-determining gene. There must be two recessives, one on each allele, in order to exhibit the trait in question.
X and Y Chromosome and sex determination.
Sex in mammals, including humans, is determined by the two sex chromosomes; the X and the Y chromosome. Females will inherit the XX chromosome and males the XY. Females only carry the X chromosome and have no Y. Consider this then the female can only pass on an X and the male can pass either an X or a Y. Therefore it is the male contribution that determines the sex of each kitten. In addition, the Y chromosome is smaller than the X and contains a smaller package of genes to pass on.
Polygenetic traits (also called quantitative traits) rely upon multiple genes linking together to exhibit phenotype. In other words, cellular information is taken from two or more inherited genes and the outcome can be seen.
A phenotype is the outward and physical look of a cat/kitten. The sum of parts all assembled; the observable structure, function, and behavior.
Genotype is the internal coded and inheritable information; the veritable blueprint or building blocks of the cat. This blueprint is written in genetic code and controls almost every cell of the body and could actually be passed on to future generations many times.
Meiosis is a special type of cell division necessary for sexual reproduction and unlike the typical cell division in order to have one from the mother and one from the father; meiosis reduces the cell in half. The cells that form during meiosis are gametes. Male gametes are sperm and female gametes are ova. They are the actual egg cells. When the gametes fuse that is fertilization taking place and the chromosome, at that time, is restored to the diploid arrangement in the forming offspring.
Meiotic drive is of special interest to those Savannah breeders who work with the filial generations and is one school of thought as to why we have sterile males at those generations. A transfer of genetic information, during meiosis, that is not reciprocated. In others words, the male genes do not get all of the cellular information they need to be a complete and fertile male because, in this case, the female information transmitted is more fit.
Haldane’s Rule “When in the F1 offspring of two different animal races, one sex is absent, rare, or sterile, that sex is the heterozygous sex.”
What does this mean? It simply means the sex that has the different chromosomes, i.e. the XY male as compared to the XX female is sterile because the XY acts as a recessive gene. As you recall from the recessive gene earlier in this chapter, it takes two recessives to trump a dominant.
Haldane studied hybridization and he made the observation that is now called Haldane’s Rule but it is now known it covers a broader range than just the sex chromosomes. Currently, there are other theories based on the Rule such as meiotic drive above and others covered briefly below.
Dominance Theory is one that may affect Savannah breedings in that the incompatibilities may come from cellular information for fertility may be at different loci (see locus above) and therefore not translated correctly resulting in infertility.
Large-X Effect Where male sterility evolves quickly on the X chromosome and accumulates a high number of recessive mutations which cause the sterility. It is a theory that if a hybrid is bred in the other direction, (in the case of the Savannah, breeding a female serval to a male domestic or male Savannah) there would be a higher incidence of female sterility and male viability.
Eumelanin is the black or dark brown bands of the agouti hair on a tabby cat.
Phaeomelanin is the red, orange or yellow alternating bands. These bands vary widely from cat to cat depending on the saturation of color.
Agouti and Non-Agouti gene discussed together. Simply put, the agouti gene is what allows spotting and striping of cats. As the hair grows, even before it reaches the level of the skin, the body produces eumelanin and deposits it into the hair. This is a process that agouti protein controls. The agouti protein will reach a saturation level and shut itself off and the hair color will shift to the phaeomelanin color until the agouti protein regains its place and once again turns back on.
The spots and stripes are present due to a partial or total lack of the agouti protein in those areas. The non-agouti gene is recessive and believed to be a mutation in that it lacks agouti protein and appears solid. Non-agouti does carry one of the tabby alleles and is seen as ghost spotting in a young cat/kitten. The non-agouti Savannah is simply black (with or without ghost spotting) and some breeders call them melanistic or just plain mel. Note* A third pattern also exists, called the ticked tabby; however it is not an accepted pattern in the Savannah breed so we will not discuss it.
Inhibitor Gene A dominant gene that suppresses phaeomelanin pigment as the hair grows. The result is a white hair with black tips. Agouti cats inheriting the inhibitor gene will exhibit the tabby pattern. They are silver and the non-agouti cats will have a black coat with a white ground color and oddly enough the spotting pattern remains visible in that white undercoat.