Last Sunday morning, the first day of Science Week, I was lying peacefully in bed when my slumbers were iinterrupted by our hyperactive kitten, Garfield. We have had many kittens before this but none have been as lively as this little thing. This is a good thing – don’t get me wrong. I have four lively young sons who are constantly amused and entertained by him. He is a gorgeous marmalade tabby but he’s as mad as a brush. The only kitten that we had which came close to being as loopy as this guy was also a marmalade tom, called (Mad) “Max” (but his coat was white in places whereas this kitten is just marmalade tabby all over). I started to wonder if insanity was a feature of marmalade cats so googled them while still lying in bed. How did we live before we had iPhones at our every beck and call?
I was pleasantly surprised to find out that not only were cat genetics a hugely interesting and complicated
topic but that marmalade (or, more correctly, orange) cats had a huge genetic area associated with them.
A genotype is the “internally coded, inheritable information” carried by all living organisms. This stored information is used as a “blueprint” or set of instructions for building and maintaining a living creature.
A phenotype is the “outward, physical manifestation” of the organism. The relationship between the two is that the genotype codes for the phenotype. Cats have 19 pairs of chromosomes. One member of each pair comes from the Mam and one from the Dad. All along the chromosomes are genes which provide the information necessary to produce a cat. Each gene is also called a locus, indicating that it has a physical location on the chromosome. Thus, each cat has two alleles of each gene; one inherited from each parent.
There is a vast amount of information available on cat genetics of hair length, coat type, coat colour, coat banding etc. What interests me at the moment is those of orange cats…
.. The orange gene has two alleles: non- orange and orange. The non-orange allele, o, is recessive and allows full expression of the black locus. The orange allele, O, however, is however. It masks the effect of the black gene by converting a black or brown coat to orange. The ability of one gene to mask the effect of another gene is called epistasis. Further, all orange cats are tabbies because the
orange allele is epistatic to the non agouti (solid coat) phenotype. This masking occurs because the orange band of granules in the hair shaft is not visible against the yellowish background of the hair without melanin granules. The other interesting characteristic of the orange gene is that it is carried on the X chromosome, which makes it sex-linked. In male cats, this locus can normally produce only two phenotypes, black or orange, whereas in females it can produce three phenotypes: black, orange, and tortoiseshell. This is because males are normally XY (heterogametic), and therefore have only one X-chromosome. Thus, if a male carries the orange allele at all, he will be orange (OY). Females are XX, meaning
they have two X-chromosomes (homogametic). If both chromosomes carry the orange allele, then the cat will be orange. However, if she is heterozygous (Oo), her coat will be a patchwork of orange and black patches, called tortoiseshell.
Basically, only 1 cat in 4 inherits one orange gene. The others will have genes for other colors, and you get a tricolor/tortoiseshell cat, which is more common. So you get many more male oranges than female oranges, about 3:1.
Males, lacking that second X, can never be tricolors except when there’s some sort of genetic malfunction. So male tricolors are incredibly rare, and always sterile.
Now – there’s a Sunday morning’s reading with a difference.