|
|
|
|
There are many other sites explaining the genetics of coatcolour in cats, but I will do it my way anyhow. First it is necessary to explain a few terms and I prefer to use the appropriate biological terms. Genetics is all about heredity. Of course many hereditary properties, but the most outstanding is coatcolour. All hereditary properties lie on chromosomes, of each chromosome there are two, one from the father, one from the mother. On each chromosome there are many genes, a gene is connected to one single hereditary property. For any property there can be several alternatives, one alternative is called allele (for example flower colour, there can be an allele fro red and an allele for white). Each individual has two alleles for each gene, if a person has two equal alleles you will call this homozygous (e.g. two alleles for white), if a person has two different alleles we call this heterozygous (one allele white, one allele red). Is the plant in this example homozygous for flower colour it is obvious what it's frower colour will be. It is not if the plant is heterozygous for flower colour, so if it ahs one allele for white and one allele for red. The ultimate flower colour then depends on the dominance of the alleles. If an allele is dominant (always written with a capital letter) then this allele always shows. Let's say Red (R) is dominant over white (w), in a combination of Rw the flower colour will be Red, as is with RR, only in the case where both alleles are white (ww) the flower colour will be white. White is the recessive allele here (always written in a small letter). It could be that both red and white are recessive alleles, which colour will the flower be then in a combination of both, rw? Pink! Both alleles will contribute to the flower colour and the colour will be intermediate between white and red, hence pink.After this general introduction I will try to explain the genetics of coat colour in Siamese. More than one gene is involved, I will use the notation as used in the book Oosterse korthaarkatten by K. van der Wijk from 1982. For a more complete summary of all genes involved in coat colour, coat structure and hair length this German site is very excellent: Genetik für Katzenzüchter
Alleles
Name
The notation of a Seal point Siamese becomes: aa BB cscs DD oo. This means this cat has an unpatterened colour fur (aa), is homozygous for the colour Black (BB), only has pigment in the points (cscs), he has no dilution for blue (DD) and he carries no orange (oo). For clarity we leave out the notation for orange if the cat doesn't carry it. Or Seal point Siamese: aa BB cscs DD
A Agouti, patterned hair (like an Abyssinian)
a non agouti, unpatterned
B Black (Seal)
b brown (Chocolate)
b1 cinnamon
cs siamesepattern (albino-allele)
cb burmesepattern (albino-allele)
C fully pigmented
D no dilution for blue
d dilution for blue
O orange (red)
o no orange
We're dealing with a gene for coat pattern (Agouti), a gene for colour (Black), a gene that dilutes the colour (dilution) and the presence of tha orange allele that determines the colour of the Siamese cat (heredity of colour is the same in Siamese and Thai of course). The dilution allele is recessive, it can only influence hair colour if the cat has two dilution alleles (dd). If this is the case Black will be diluted to Blue and brown (chocolate) to Lilac. The gene for orange lies on the female sexchromosome (X). Females have XX, males have XY, a male can therefor only have one allele for orange.
* these are codes for Siamese, replace SIA with THA and you have the codes for Thai.
Allele combination
Colour
Colournumber
Colourcode *
aa B- cscs D-
Seal point
24
SIA n
aa B- cscs dd
Blue point
24a
SIA a
aa bb cscs D-
Chocolate point
24b
SIA b
aa bb cscs dd
Lilac point
24c
SIA c
aa B- cscs D- OO
Red point female
32a
SIA d
aa B- cscs D- O
Red point male
32a
SIA d
aa B- cscs D- Oo
Seal Tortie point female
32b
SIA f
aa B- cscs dd Oo
Blue Tortie point female
32b
SIA g
aa bb cscs D- Oo
Choc. Tortie point female
32b
SIA h
aa bb cscs dd Oo
Lilac Tortie point female
32b
SIA j
aa B- cscs dd OO
Cream point female
32c
SIA e
aa B- cscs dd O
Cream point male
32c
SIA e
A- B- cscs D-
Seal Tabby point
32
SIA n 21
A- B- cscs dd
Blue Tabby point
32
SIA a 21
A- bb cscs D-
Choc. Tabby point
32
SIA b 21
A- bb cscs dd
Lilac Tabby point
32
SIA c 21
A- B- cscs D- Oo
Seal Tortie Tabby point
32
SIA f 21
A- B- cscs dd Oo
Blue Tortie Tabby point
32
SIA g 21
A- bb cscs D- Oo
Choc. Tortie Tabby point
32
SIA h 21
A- bb cscs dd Oo
Lilac Tortie Tabby point
32
SIA j 21
A- B- cscs D- O
Red Tabby point male
32
SIA d 21
A- B- cscs D- OO
Red Tabby point female
32
SIA d 21
What if you have a Seal point queen and you want to bring her to a Lilac point stud. Which colour kittens can you expect? This depends on the genetic background of the colour, is the queen carrier of the dilution allele, or of the brown allele? If the queen is aa BB cscs DD (just Seal point) and you use the stud service of an aa bb cscs dd (the Lilac point stud), the result will be kittens with aa Bb cscs Dd, or Seal point and carrier of dilution ('blue') and brown (chocolate). On the next page I'll give several crossbreeding tables, to make it still clear I will use abbreviations. These abbreviations were borrowed from the book Houden van Siamezen by Kik van Eijsden, 1977.
Crossbreeding tables - Tabby Points
This page is not complete, but I'm available for questions and comment, did I forget anything or are there any errors? Mail me: elinegeertsema@solcon.nl
Sources:
Houden van Siamezen by Kik van Eijsden from 1977 (Uitgeversmaatschappij Holland in Haarlem, The Netherlands)
Cattery Elvëa Mëoi | Queens | Studs | Godfathers | Kittens | Genetics | Shows | Links
Cattery Elvëa Mëoi
elinegeertsema@zonnet.nl
Date Last Modified: 06-06-2007
Copyright Eline Geertsema