During
the development of the embryo there is a
point when the chemicals responsible for the color of the coat are flowing
into the hair shafts. This is very technical and it is probably not
necessary to understand the details of this process for our purposes.
The important thing to remember is that it is a process and how
that process happens effects the out come of the color of the hair shafts.
The color is effected by how rapidly (or slowly) the pigment
is formed and deposited in each hair individual shaft. The more rapid
the process the deeper the color, the slower the process the lighter the
color. So, the process dictated by the agouti gene for the formation
of color in the hair shaft is an "on-off" system of synthesizing
the pigment creating the bands of color on the hair shaft (usually dark
pigment near the tip of the hair shaft with varying depths of dark and
light "striping" down the length of the shaft). The difference in
the color is caused by the speeding up ("on") and slowing down ("off")
of this process responding to the message from the agouti gene.
The width of the band of the various shades of color is determined by how
long the process was "on" or "off".
The gene for the agouti banding is dominant. The symbol for agouti
is: A. (A capital letter is always used to indicate a dominant trait.)
Therefore all tabbies have the A gene, as it is an important
part of the expression of the tabby pattern. It is the canvas that
shows off the expression of the tabby markings. In art, we are taught
that you can't show dark without light or light without dark. The
darker tabby pattern shows up because it is against the light agouti background. |
The
tabby pattern or markings occur when the T gene is expressed causing
certain
hairs to become solid. What actually happens is the T series
genes stop the formation of the yellow in the specific hairs that
determine the pattern indicated by the particular T gene carried by the
individual, causing these hairs to fill solidly with the melanin granules
producing melanistic solid spots, stripes,
marble, or classic tabby pattern markings against the agouti background.
So, the T series only determines which tabby pattern
will
be expressed.
The tabby genes are symbolized by: Ta
(Abyssinian type of tabby which is dominant over mackerel), T (mackerel
or striped tabby which is recessive to Ta
but dominates tb), and tb
(classic or blotched tabby) - this is also where our Bengal marble
tabbies fall (the symbol I use for marble is tm
but you should know that there is not a "formally" assigned gene symbol
for this trait - but it is the one I personally use). So, a marble
Bengal is symbolized by: A_tmtm
and
a mackerel tabby would be A_T_. (Note, it is common genetic practice
to use a single capital letter with an underscore to indicate the recognition
that we probably do not know if this animal is pure for the dominant trait
or carrying a possible recessive.)
The inheritance of the Bengal spotting as well as the other forms of domestic
spotted tabbies are not completely understood. Robinson's book speculates
that the spotting (domestic spotted tabbies) is likely a modifying gene
that acts on the existing tabby gene. He tentatively gave this spotting
gene the symbol: Sp. (I personally use Ts for
the spotting gene as we know it is dominant and I've seen little
evidence that it is a different allele.) |
|
Agouti
vs Ticking
|
OK,
so what's the difference? We hear breeders talking all the time about
the negatives of "ticking" and how we need to breed away from it (clear
coats). But, we've just seen that without the agouti ticking/banding
on the background hairs you wouldn't see the pattern at all. As a
matter of fact, the non agouti gene (aa) produces an all black cat (or
a solid for whatever color the individual cat would be -- black in most
Bengals) by taking the yellow out of the background hairs so that they
are now solid, too. This creates a black pattern on a black background.
This is the melanistic Bengal you may have heard about.
When the solid color hairs are being formed (this is the marking or pattern
area) the color pigments need to be deposited in the hair shaft quickly
and evenly to produce an even dark color. Ticking is hairs
within
the markings that are not solid black as desired. We've
also heard about "black to the skin". This is the same principle.
We are looking for hairs that do not fade out getting closer to the skin.
This requires selective breeding of individuals that have the most solid
markings (and black going the farthest down the hair shaft). What
we are probably increasing are the genes that control the uniformity
of the depositing of the melanin in the hair shaft by controlling the
speed and how long the synthesizing stays "on".
While we will never eliminate agouti ticking from the background area,
the amount and width of color bands on the background hairs can certainly
be modified by selective breeding. The rufousing so much sought after
in our Bengals is thought by Gloria Stephens to be poly (several unknown)
gene modifiers acting on the yellow portion of the agouti in effect "brightening"
them. In Abys the more bands of agouti the better. Just the
fact that Aby breeders can increase the number of bands on the hair shafts
by selective breeding, proves that the opposite is possible, also, by selective
breeding.
In Bengals to goal to a clear coat means the agouti hairs need to have
the black portion be minimal and not at the very tip o the hair.
When the hair for the background ends in black the pattern looks muddy
or blurred. |
|
In
Summery
|
|
Agouti is the banded hairs of the background hairs of tabbies or the overall
hairs of the Abyssinians and is an integral part of the tabby pattern.
Ticking is the hairs within the dark marking portion of the tabby
pattern that spoils the look and contrast of the solid marking area. |
|
Last
Lessons question . . . .
|
If
you cross your brown spotted boy with green eyes with your blue eyed snow
(Lynx point) queen, is there a possibility any of your kittens will be
snows like mom with the dad's green eyes? Why?
The answer is no. It is the 'why' that is more difficult many.
A Lynx point snow is part of the Albino
series. Albinism causes a reduction (or elimination)
in pigment
causing the genetic color(s) to be seen as lighter or to optically seem
to be a different color. The eye color in the brown spotted tabby
is produced by a gene for the eye color, as is the color of his coat.
The Seal Lynx point is genetically a black cat probably with amber or green
eyes but with the pigments reduced in coat
and
eyes (a mutation
of the full color gene) so that they
appear blue due to the reduced
amount of pigment in the iris. Therefore the brown spotted will dominate
the Lynx point and if the BST carries for Lynx point there will be the
possibility of Lynx point kittens; but, they will always have reduced pigmentation
on the whole animal including the eye color causing the eyes to appear
blue and the "pointed" colors to be expressed.
Here's your challenge question for next week: Can Lynx point carry
black? You must explain your answer. E-mail
me your answers. |
Lesson
Two
Making
Snow Genetics Easy........
|
