BASIC GENETICS

COLOURS

There are in fact only two colours in the Birman, or any other cat for that matter, and those are BLACK and RED.  All other colours are mutations or modifications, either to the pigment itself, or the arrangement in the hair shaft.

The gene responsible for the Siamese pattern of the Birman, is a member of the albino series.  Its effect reduces the amount of pigment in the pigment granules, giving the appearance of a paler point colour, such as seal, to its corresponding full pattern of black.

BLACK (B)

Chocolate (b) is a mutation, which causes the elongation of the spherical black (B) (seal) pigment granule, making it oval and therefore creating the appearance of being paler. Cinnamon (bl) is a further stretching of the granule giving it the illusion of being paler yet again.

The following chart shows how Cinnamon is inherited. It is recessive to chocolate as chocolate is recessive to Seal or Black. Chocolate and Cinnamon cannot be carried simultaneously, as it is found at the same locus.

PURE SEAL (BB) X CHOCOLATE CARRYING CINNAMON (b bl)

RED (O)

The red gene is a sex linked gene carried on the X chromosome, of which males normally only have one (XY) and females two (XX).  Therefore the male can only have one red gene on his one X chromosome, where the female can have one red and one non-red (tortie) or two red.

Red masks the presence of seal, chocolate or cinnamon, when it converts all black pigment to red.  The non-agouti (unbanding) gene acts only on black pigment, therefore hairs containing red pigment will always have agouti banding.  As a result there is no visible  difference between red and red tabby, they will both exhibit the tabby pattern.

DILUTE (d)

Dilute colours come about when the normal densely arranged pigment granules of the seal, clump up and scatter in the hair shaft causing a dilute effect.

PATTERNS

TABBY (Agouti) (A)

Tabbies arise from a combination of two separate patterns, each acting independently.  The tabby pattern itself, responsible for the solid  coloured barring in the mackerel (T)and blotched (t) tabbies, and the agouti pattern (Ta), (as seen in the Abysinnian) in which the guard hair shafts, in between the tabby pattern, are composed of a dark tip separated by a yellow band (known as the agouti band) followed by a dark base.

Birman breeders need not concern themselves with the type of tabby pattern their cat may be, as barring is restricted to the points, making pattern changes less obvious, however, the abyssinian tabby, may not display an acceptable degree of barring, due to the fact that almost all of the guard hairs are banded and barring has been virtually eliminated.   While undesirable for the exhibition tabby, it can be used to advantage in reducing  barring in reds.

PLAIN (a)

Plain point or non-agouti results when the agouti bands have been eliminated from the hair shafts located between the tabby bars, thus creating the appearance of solid colouring.  This can be substantiated by the ghost barring often noticeable in kittens.

The saying "all cats are tabbies" actually means all cats have the tabby barring pattern, not all have the agouti pattern.  The confusion lies in the fact that tabbies must have both patterns to be expressed as tabbies i.e. all tabbies are agouti.

SILVER (I)

Silvers possess the dominant gene known as the inhibitor gene, so called because of its nature of inhibiting the development of pigment in the more lightly pigmented areas of the coat, such as the undercoat towards the roots and the agouti or yellow areas of the coat.  Consequently the tabby pattern stands out against a white background.  The degree of silver is influenced by polygenes and may vary from low to high grade.

MODIFIED COLOUR AND PATTERN COMBINATIONS

Tabby and silver are dominant genes, therefore they only need one parent displaying them in order to be produced, whereas to produce a dilute the recessive gene must be carried by both parents.