CAT GENETICS

"What’s Really Happening?"

David &Jacqui Richardson , RAGAJAC Ragdoll CATTERY.

Breeding without an understanding of genetics is like following a road without a map. All is well until you reach a crossroad!

Gaining a basic understanding of genetics, empowers you, the breeder, to be able to make an informed decision about which road to take.

Learning about genetics can be both exciting and rewarding. It is a powerful tool and will help you achieve your breeding goals generations earlier and minimise "hit and miss" matings.

Getting a handle on the basics is not difficult and we hope to lead you through to a better understanding of genetics with this series of articles.

Basic genetics was worked out by a Monk called Gregor Johann Mendel in the 1860’s using pea plants. His comparatively simple methods are what we still use today.

THE GENE POOL IS LIKE KIDS' BUILDING BLOCKS

The genetic makeup of a cat is contained on 19 pairs of chromosomes. One chromosome of each pair comes from the mother and the other one from the father. (Humans have 23 pairs of chromosomes).

The Double Helix

Each chromosome is basically a very long twin intertwined spiral molecule called DNA - the famous "double helix" of Watson and Crick.

The beauty of DNA is that it can be broken up into segments and recombined in a different order just like a tower of children’s plastic building blocks can be rebuilt in a different order or some of the blocks replaced by other blocks from another pile.

Sperm and Egg Formation

Consider that one of the mother’s chromosomes consist of a tower built of blue, green and red building blocks and one of the father’s consist of a tower of yellow, black and pink building blocks. When the sperm and the egg form (not meet), in the father and mother respectively, the chemicals forming the towers blocks shuffle themselves and then recombine in such a way that each and every block is unique. This means that every sperm and every egg is a unique individual each containing 19 towersof blocks (chromosomes).

Fertilisation

So, the sperm has 19 towers of blocks and the egg has 19 towers of blocks and when the sperm and the egg get together (fertilisation) the appropriate towers find each other to become 19 matching pairs of towers, the full compliment needed for a normal cat.

Chromosomes and Genes

In genetic terms we call the towers chromosomes and we call the building blocks genes. The pairs of coloured blocks (one from Mum and one from Dad) control the final characteristics of the kitten.

Genes and Alleles

Lets say - in the twin recombined towers found in the kittens embryo after fertilisation, the second block from the bottom controls hair length. Then the kittens hair length is controlled by the action of the two blocks second from the bottom in the twin towers of that chromosome pair.

This pair of blocks would be called the gene for hair length and each block of the pair is called an allele. When the two alleles get together, they are called a gene.

Dominant and Recessive

Many alleles are either dominant or recessive. In the hair length case (short or long hair) short hair is dominant over long hair. This means that if a cat gets a short hair allele from one parent and a long hair allele from the other parent, the kittens do not have medium length hair as you may think, but will have short hair because short hair is dominant over long hair.

A dominant allele is given a capital letter symbol and a recessive allele is given a lower case letter so, the recessive long hair allele is written "l" and the dominant allele for short hair is written "L".

When the two alleles get together to form the gene in the example above, it is symbolised by "L l". ("L" stands for length not long).

Not all genes are dominant/recessive.

It should be noted that not all alleles form these dominant/recessive pairs. Many have what is called mixed or incomplete dominance resulting in an unpredictable mix of the two characteristics. e.g. the white spotting gene.

SEX CHROMOSOMES AND SEX LINKING.

A cat has 19 pairs of chromosomes. 18 are known by numbers (1 - 18) and the last pair is special and is called the sex chromosome. This chromosome may be in the shape of an "x" or an "x" missing an arm which is called the "y"chromosome. In this chromosome pair one x may join with another x or with a y but two y’s cannot join. The xx pattern gives us a female kitten and the xy pattern gives us a male kitten.

Several interesting points follow from this.

Males control the sex of the offspring. This is because the mother can only donate an x chromosome to the pair but the father can donate an x resulting in a daughter (xx) or a y resulting in a son (xy).

Girls have more genes than boys. Because the male has one arm missing off his x chromosome to make a y shape, the female carries more genetic material than the male. The arm causes the female to be a female, whereas the default is the male.

What else is on this magic arm? There are other genes on this arm apart from the genes causing the sexual characteristics of the female. These other genes are said to be sex linked because they cannot be carried by the male who is lacking this genetic material.

The Orange Sex Linked Gene

In the cat, the best known sex linked characteristic is the orange colour gene, (O). This gene is carried on the arm of the x chromosome which is missing in the male. Therefore the orange colouring can only be inherited from a female cat. It is a gene of neutral dominance and therefore it is not fully seen in females unless both the x chromosomes of the female carry the orange, however in the male it is unopposed because the y chromosome of the male, is missing the arm which carries the gene.

Orange Boys and Tortie Girls

Because it is non dominant, a female cat (xx^o) carrying the O gene on one of it’s x chromosomes has areas of orange and areas of brown or other colours in it’s coat, this we know as a tortoiseshell. A female carrying the O gene on both the x chromosomes (x^ox^o) will be all orange and of course, as previously stated, an x^oy male will be orange and an xy male will be a "wild colour" with no orange.

Tortie Boys?

The only way you can get a male tortie is with a genetic malformation (xx^oy) in other words having an extra chromosome. These tortie boys appear as males but are almost always infertile.

Therefore there are many more orange male cats than there are female, and an orange dad can’t have orange kittens unless his mate is also carrying the orange gene.

PHAEOMELANIN AND EUMELANIN.

In cats there are two different gene groups which bring about the colours of the cats. These are the Eumelanin gene groups which produce black and brown pigments and their dilutes (blue, choc, lilac etc) and the Phaeomelanin group which bring about the red and yellow pigments and their dilutes (cream etc).

Original Ragdolls do not carry Red

Traditionally Ragdoll cats are Eumelaninitic cats, ie. Red and yellow are not contained in their gene pool, however, recently Phaeomelaninitic genes have been introduced into the breed producing Ragdolls with red colour, flame points tortoiseshell etc. It should be noted that all orange cats have tabby markings.

CONCLUSION

Gaining an understanding of Mendelian genetics gives breeders a greater probability of outcome and we believe it is well worth the time and effort taken to gain a grasp of this interesting subject.

LOCAL RESOURCES

People you know who will have a reasonable understanding of genetics are your vet, your doctor and your local High School biology teacher. These people may well be happy to spend a few minutes explaining genetic concepts. Libraries and encyclopaedias will have good information on basic genetics.

David and Jacqui Richardson ......email...........

ragajac@bigfoot.com