genetics101

Genetics 101
Lesson 2
Understanding Snows . . .

Just like with last weeks lesson, snow genetics is probably a bit advanced for just a second lesson. But, there are so many questions about the snows and most of you have the "basics" down pretty well. [If you need anything explained differently or broken down, I would be happy to.]
The first thing I think is needed with the snows, is a bit of a review on colors and other factors that effect the appearance of color in cats. Our ideal Bengal is a black cat (BB) with full color (C_DD), ii [non inhibitor] and is a tabby (AAT^s_ or AAt^mt^m). [The ideal snow Bengal would be: AABBc^sc^sDDiiT^s_(or or c^bc^s or c^bc^b t^mt^m)]. In other words, our ideal Bengal is a Black cat, not carrying any recessive [like chocolate (bb), cinnamon (b¹b¹), melanistic (aa), etc] with full color expression (except if it is a snow), carrying no dilute genes (blue), is not silver, is agouti for tabby (either spotted or marble).

    *** FYI The example above in red, of the genetic symbols
    demonstrates the preferred order in which to present them:
    (alphabetical).] ***

Now I said our ideal Bengal is a black cat, so why are they called brown spotted tabbies? Because years ago everyone called the tabbies
brown (because that is the color they looked like); however, when the
knowledge of genetics became better known, the European fanciers began using the correct genetic term, but we Americans continued to use the traditional term of "brown tabby" because that is what we were used to. Even registries like TICA that claim to be "genetic" registries use the
term 'brown'; yet, if we truly had a brown tabby that would be chocolate
(bb), and we all know that chocolate is undesirable in our Bengals. So,
technically our Bengals should be black tabbies in a spotted or marbled pattern.
Ever wonder why we insist on black tail tips and paw pads? This is to verify that we have a genetically black cat under whatever else is going on with it's appearance. Check out your seal Lynx point, the tail tip will look black (but, if placed right next to the black tail tip of a BST or BMT you can see that it is slightly lighter which is the effect of the albinism). This is why all "snows" approved for championship status are referred to as "seal". Seal is the darkest of the Siamese colors indicating a genetically black cat with the "pointed" gene (c^s). [Note: a "snow" with a truly black tail tip is a silver. Which is also a genetically black cat. More on silver next week.]

* * *

         As a newbie, I asked a TICA official at a show why "seal" had to
preface all "snow" colors. It seemed to me that if they were all "seal"
then we could drop the word "seal" and it could be assumed and it
would shorten the color name. This person (who, I'm sure thought this
was a silly question or didn't really know the answer) said that "was how
it had to be because they were from the Siamese". It was another 2
years before I found out that even in Bengals there are chocolate minks
(and Lynx and sepias) and there were blue Lynx (and minks and sepias)
and there are silver Lynx (and minks and sepias) and you registered your
"snows" as seal (only if they are seal) to distinguish them from other colors.
         Anyway, don't feel like you're the only one who doesn't know
something; and, I promise to give you the best answer I can, and not
give you "the brush off" when you have a question. If I don't know the
answer, I'll find it out for both of us. All of us were newbies once and
all of us are still learning.    <gg>

* * *

         Lynx point, mink, and sepia are the result of a mutation of the C gene series for full pigment (if you think of it as full pigment instead of full color I think it makes more sense). Therefore, this is not color
inheritance but the inheritance of full or reduced pigment amount. When the C gene mutated, a series of albino traits were created. Full albino with the pink skin, pink eyes, and clear almost transparent white fur is symbolized by cc (and is recessive to all the C series). [In felines the pink eyed or true albino is extremely rare.] The individual who is albino looks like they have "pink" eyes and skin because of the lack of ANY pigmentation in the eyes and skin (and hair) which allows the blood just below the skin and in the retina of the eye to show through creating the pink color.
     The blue eyed albino (non pointed) is symbolized by c^ac^a. The "pointed" genes seen on Siamese, Burmese, and Tonkinese are symbolized: c^sc^s (Siamese), c^bc^b (Burmese), and c^bc^s (Tonkinese). These are the same symbols used for Lynx point (c^sc^s), sepia (c^bc^b) and mink (c^bc^s) in Bengals (the genetics didn't change - the genes and process are exactly the same). All of these colors are albino to one degree or another and the term "pointed", while usually used to indicate Siamese or Lynx points, also applies to the Burmese or sepias.
         The "pointed" genes are effected by temperature. When you see a
Siamese, the genetic color of the cat is the color of the face, paws, ears,
etc( the "points"). This color is only shown on the cats colder areas of the body (where there is less circulation) due to the temperature. The albino action has a greater degree of effect on the warmer areas of the body causing the pigment to not develop in these warmer areas. It is easier to understand the action itself than the mechanism of "how" it works. And, how it works is not as important as remembering that it is part of the package of dealing with snows.

* * *

If c^s & c^b are reduced pigmentation, what is the difference between that and the D (dense/dilute) series genes? The C genes are an albinism and where the gene has the most effect, the cat is albino in that area of the body. The D gene governs the density of the distribution of color pigment in each hair shaft. So the black cat with the gene (dd) for reduced density appears blue (black pigment is spread out less densely throughout the hair shaft allowing more light to pass through causing these hairs to appear lighter). ex: add water to your black watercolor paint and then paint with it - looks gray right? - but you only used the black paint and plain water to create the look of gray -- same idea. If the cat with the dd gene is genetically red instead of black, then the appearance is cream. This is often called "dilute" and this is an excellent description of this trait (in Bengals a kitten with the dd or dilute genes is called "blue").

* * *

         To understand how these traits are inherited, it helps to go back to
our high school biology class. Remember the Petunias? When the white Petunia was bred with the red Petunia, pink petunias resulted. IF the red Petunia had been dominant, the F₁ generation would have been all red carrying white recessively (white would not have been seen). BUT, in this case, the white shows in the F₁ generation by reducing the red to pink (both the red and white color are exhibited in this generation - none is hidden as in a full dominance.) When the pink Petunias are bred to each other in the F₂ generation a ratio of 1:2:1 results as would be expected (25% red : 50% pink : 25% white). This is an example of incomplete dominance (also called blended characteristic or co-dominance).
         The "brown" colored (BBC_) Bengal dominates ALL "snow" colors, so that is easy - no new rules. BUT, when you breed the snows to each other (or a brown carrying), that gets interesting. During the following discussion, try to remember the Petunias and "think pink" - see if it is easier to understand. Also, remember: this is the inheritance of who has more (c^bc^b), less (c^bc^s), and lots less (c^sc^s) pigment (these are all still black cats).
         If you "think pink" and substitute a red Petunia for the sepia, you'll
see that there will always be red to show through (be expressed). So, if
red is bred to red; only red will result (white can't be "carried" without
changing the appearance of red to pink), bred to pink; only red and pink will be produced and, if red is bred to white, only pink is produced. No time in breeding red did you get white. It is the same principle with the sepias. They can't produce a Lynx point.

Incomplete Dominance Demonstrated by Petunias:
Red (rr) X White (ww)

Pink (rw) X Pink (rw)

Red (rr) X Pink (rw)

Applying this to the Snows:
Now if you substitute Sepia (c^bc^b) for red, and mink (c^bc^s) for pink,
and Lynx point (c^sc^s) for the white you get the same results.

Sepia (c^bc^b) X Lynx pt (c^sc^s)

c^bc^s

Sepia (c^bc^b) X Mink (c^bc^s)

c^bc^b

c^bc^s

Mink (c^bc^s) X Mink (c^bc^s)

c^bc^b

c^bc^s

c^sc^s

The thing to remember with these colors is that nothing is hidden OR "carried". I'm going to go out on a limb here. We've repeatedly said eye color is not an indication of mink or sepia. However, with a solid knowledge of your pedigree, of the parents, and the cat in question's adult mature eye color, these should be able to give a very good indication of the amount of pigment that particular cat has - and that should be a decent indicator of the cats proper color. Test breeding would verify or disprove whether you're right or not. I personally believe that it is inexperience and lack of understanding of the inheritance of an incompletely dominant trait that is causing the confusion. I, also, think we forget that it is the amount of pigment in the eye and fur, not a color, we are dealing with.
There is also the temperature sensitivity of these genes whose expression (and its effect) is yet to be clarified as to what extent it applies to our Bengals. We seem to have bred away from this to some degree just by selective breeding. (ie: the lack of marking expression on the sides and the old "pointed" Lynx point Bengals are no longer the norm & the Lynx points without "points" and with the contrast we're seeing now, would not have otherwise developed).

* * *

A word about brown Bengals carrying a "snow" color. I've heard the theory spoken as fact by a breeder considered 'knowledgeable' in snow genetics, that she can tell if a brown is carrying snow by looking at the eyes. This is NOT science. When a gene dominates the action of another gene, the recessive gene does not act at all. (This is all at the cell level so there is nothing the animal would exhibit to give any indication of what is or is not carried in the cells.) Example: If you are a genetic carrier of a disease, you will not know it without DNA testing. Blood tests or other testing will not show it - because you don't have the disease. You have a gene that can pass it on, but you don't have the disease itself. A brown Bengal that carries a snow gene and a brown Bengal that does not will look exactly alike, and only by passing on the recessive gene on will you know it is there.

* * *

Answer to last lessons question: Can Lynx point carry black? I admit
this question was a bit tricky, but some of you "hit the nail right on the head" anyway. First of all, remember that Lynx point is not a color and
therefore can have any color at the color locus (location). Bengals should be genetically black, as we've just learned, so would not be "carrying" but would be black. So, the answer to that is: no.
I meant the question to be: can they carry melanistic, but did not ask it that way. However, some of you answered it the way I meant it -- so thank you for reading my mind! The answer to this part is: yes. Again, because a melanistic Bengal is a "solid" Bengal or one who has no agouti gene (aa instead of AA or Aa), non agouti can be carried by any color cat and is even found in the wild (ie: black leopard). So, you could get a solid black kitten in a cross with Lynx point and brown when both carry for non agouti. However, if the non agouti gene were to show up in a cross between 2 Lynx points, (that were both carrying) you would get a very pointed Siamese looking Bengal (without the agouti gene you would not get the spotting or marble pattern and the tabby markings on the "points" would not be there).

This lessons question: You are expecting a litter of kittens from your a
beautiful seal Lynx point spotted queen (whose mom was a mink). The sire of her litter is a very nice mink marble boy (with Burmese 5 generations back on his father's side). Is it
possible to have sepia babies from this cross? (Careful this one is tricky.) As usual you must explain your answer. E-mail me with your
answers. <g> Do you have a suggestion for a question? E-mail that to
me, too.
Next week: Silver Bengals & Other Colors

Additional Checkerboards of
Crosses Involving "Snows" . . .

A brown Bengal carrying Lynx point (Cc^s) X with a mink (c^bc^s):

Cc^s	Cc^b
c^sc^s	c^bc^s

50% of litter will be brown (50/50 carrying mink/Lynx point)
25% of litter will be Lynx point & 25% will be mink
Note: Even though the phenotype will be identical, the browns in this litter will
have different genotype. There is no way to know which browns carry what.

~ ~ ~ ~ ~

A brown Bengal carrying mink (Cc^b) X with a mink (c^bc^s):

Cc^b	Cc^s
c^bc^b	c^bc^s

50% of litter will be browns & (with 50/50 carrying Lynx point or mink)
25% will be mink & 25% will be sepia

~ ~ ~ ~ ~
A brown Bengal carrying mink (Cc^b) X with a Lynx point (c^sc^s):

Cc^s	c^bc^s
Cc^s	c^bc^s

50% of litter will be browns & all will carry Lynx point
50% of litter will be mink

~ ~ ~ ~ ~

Brown Bengal carrying mink (Cc^b) X with brown
Bengal carrying Lynx pt (Cc^s)

CC	Cc^s
Cc^b	c^bc^s

75% will be brown 25% homozygous for brown & 25% carrying Lynx pt.
25% carrying mink and 25% of litter will be mink

>^{^}..^{^}<

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