The Red Series

What does sex linked mean?

All 19 of the cat chromosomes are identical pairs except one pair -the sex chromosomes.  The two sex chromosomes are labelled X and Y, basically the Y chromosome is an X with the end chopped off.  Males have an X and Y chromosome and females have XX.  The locus for the O gene happens to be positioned alongside the chopped off piece on the Y chromosome.

          X  X         X  Y

         female       Male

Therefore a male can only have one O gene.  This is not a problem it just means that which ever gene they have is expressed.  So if a recessive gene is on the X chromosome it will be expressed and the male will not be a red.

Females have 2 O genes.  If they are OO the cat will be red if they are oo the cat will be non-red....

...however the naughty torties break Rule 3!  When a female cat is Oo a tortishell is produced, that is a mixture of red colours and base colours.  The colour of the tortie will depend on its basic colour genotype ie what combination of B,b,bl it carries.  Remember the "true" genetic colour of a red series cat, other than a tortie, is masked by the O gene- this phenomena is epistasis.  This means a red, cream or apricot cat can "carry" all sorts of colours many of which will only be apparent if it is bred with a cat that dosen't carry O- a nice surprise for some unsuspecting breeders!

If you look at the photograph of Mel (a cream) you will see the other interesting effect of the Red gene.  Mel has Tabby markings even though he is not genetically a Tabby - all red series cats have this pattern, it is another element of the epistatic effect -a true red tabby and a self red cannot be distinguished by looking at them. 

Possible Red genotypes

Note (-) means any gene of series eg Dm- means DMDM or DMdm.