Cat Breeding

For Dwarf Cats

Cat breeding is something that buyers should ideally know a bit about as it allows them to ask the right questions when buying and to understand more about this interesting breed.

Genetics are complicated. Not enough is known about the dwarf gene and how it is transmitted so in a discussion of breeding in relation to dwarf cats we are not talking science. There is a degree of “hit and miss”. All the more reason then for dwarf cat breeders to be cautious and vigilant and to not become “kennel blind”. Kennel blind describes breeders of cats or dogs who have not been able to keep a balanced, open and objective view of what they are doing in their breeding program at the expense of the cats.

The Dwarf Gene

The Dwarf Cat Association (DCA) say that it is believed that an “achondroplasia-like gene” is the cause of dwarfism in the Munchkin breed and therefore is the cause of dwarfism in all cats bred from that breed. Remember the Munchkin is the founding breed from which other dwarf cats are bred. Also note that the DCA says “it is believed” (i.e. not enough it seems is really known about this breed). A lot is known about achondroplasia, however.

Achondroplasia is a bone growth disorder. A strict translation of the word “achondroplasia” means “without cartilage formation”. However, the problem is not about the failure to produce cartilage during growth, but of bone (particularly in the legs of the cat). How does this come about?

It comes about because of the Mutation of a particular gene. “Mutation” means a change in the structure. The particular gene concerned provides instructions during the growth of the animal regarding the making of a protein involved in the development of bones. The instruction is for the control (limiting) of the production of bone from cartilage. It is believed that because of the mutation the instructions are irregular resulting in the protein produced to be “over active”. Being over active it limits too much the formation of bone from cartilage. The result: short limbs.

The mutated gene is “autosomal dominant”. “Autosomal” means a non-sex determining chromosome and “dominant” means that an abnormal gene from one parent is capable of passing on the condition even though the matching gene from the other parent is normal. The abnormal gene “dominates” the pair of genes.

The Breeding

Going back to the first generation, if you breed from a dwarf cat and a non dwarf cat (just one parent has a dominant gene defect) each offspring has a 50% chance of inheriting the disorder. So if there are 4 kittens 2 will be dwarf kittens. The other two will have normal leg length.

In practice how do dwarf cat breeders work? They work with Standard dwarf cats (S) and Non Standard dwarf cats (NS). A litter of dwarf cats is not populated entirely by short legged dwarf cats.

Standard dwarf cats {Munchkins} carry 1 copy of the dwarf gene. Non-standard Munchkins {NS?} carry NO copies of it at all–they may have standard parents or one standard parent, but they inherited a normal {non-dwarf} gene from each parent making them complete non-carriers of the gene. This gene is generally not variable in its expression. If a cat inherits one copy, it will ALWAYS be a dwarf. The reason most Munchkin litters contain both short and normal legged cats is because all standard Munchkins have only one copy of dwarf and therefore do not breed true for it. So any litter can have both. (src: wynnyelle – thanks)

Once you have started breeding you will have NS and S. Ss are sold and NSs are given away or sold. Breeders have the choice to either breed S to S or NS to S in order to produce dwarf cats.

When you breed NS to S, 50% are dwarf kittens and the remainder non dwarf kittens.

Breeding Standard to Standard it is claimed results in 2/3rds dwarf kittens and the remaining 1/3rd are long legged. BUT, when a kitten in the womb inherits both dwarf genes from her parent she is homozygous and it is though that this kitten will not survive in the womb, die and be “absorbed” into the body of the mother.

If this is the case it may explain the 2/3rds 1/3rd breakdown mentioned above. In theory if S and S mate all the litter should die before birth. This in not the case. It seems that breeders do not know why. No criticism intended as breeders are concerned about the health of their kittens and breeding parents.

But as you can see breeding S to S produces more dwarf cats and is therefore more profitable. Caveat: if you breed from a too narrow gene pool you are probably “kennel blind” and your breed will “die out” through ill health.

The debate, therefore, is whether it is better to breed by mating NS to S or S to S. The latter produces more dwarf kittens but it could be argued that this policy is bad for the health of the breed and therefore detrimental in the long term. Different breeders have different opinions.

Dwarf cat breeding is not that profitable it seems. Breeders do it because they love the work and cats. They are pulled between making money, maintaining a healthy gene pool to ensure long term viability of their breeding program and the need for short term financial gain to run the cattery. In short dwarf cat breeding and cat breeding in general is a complicated business.

Sources:

  • Dwarf Cat Association
  • University of Maryland Medical Centre
  • Genetics Home Reference
  • Munchkins.com website
  • The University of Utah, Genetic Science Learning Center
  • All photos this page © ckaihatsu webshots.com



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