Genetics
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The Basics
Genetics is the passing of genes from mother and father to child. Or in this case, the passing of traits that creates a specific color of rabbit from parent to offspring. One trait is inherited from the sire, and one from the dam to result in a specific coloring of the offspring sometimes different from that of the parents. A gene is just a word that describes the instructions that are passed from parent to offspring for a specific characteristic (in this case, colour). So, how are genes passed from sire and dam to offspring? Each reproductive cell has 22 chromosomes, exactly half of the genes that every other cell in your rabbit's body has. So, when an egg and a sperm are joined, the zygote (the unformed baby rabbit) has 22 chromosomes from each parent, giving the offspring a total of 44 chromosomes. Each chromosome holds instructions for what the rabbit will look like, act like, and do, from temperament to what color a rabbit is , are all contained on a tiny chromosome. A group of gene s gather together to form a chromosome, and when the chromosomes group, they create a strand of DNA. Throughout learning about genetics, it is important to keep this bit of information in mind. If this all went right over your head, keep reading, or you can e-mail me and ask me what I'm talking about!
The B and D genes
In rabbits, there are quite a few genes that relate to the color, however only two are used to create the black, blue, chocolate, and lilac. All other colours are merely a variation of one of these four colours. Actually, it is possible to narrow it down to just black and chocolate. The first gene is the "B" series, which gives us the Black and the Chocolate colored rabbits. The black gene is represented by a capital "B", so it is dominant (which means that it covers up the other gene that it is with, making a rabbit black no matter what the other gene is). The chocolate is written with a lower case "b". So a black rabbit could have a genotype (that is the list of genes that are known) of either BB (which is called Homozygous, meaning that both of the genes are the same, both BB or both bb), or Bb (which is called Heterozygous, or two different genes paired together). Because a B is dominant to a b, no matter what, if a B is present, the rabbit will be a black. Chocolate can only be written as bb.
The next (and last) groups of genes is called the Dilute series, which is what gives us blues and lilacs. A blue is a diluted black, and a lilac is a diluted chocolate. The dilute series is represented by a D, when either DD or Dd is present with either BB or Bb, the result will be a black rabbit. When bb is present with DD or Dd, the rabbit will be a chocolate. If the rabbit has BB or Bb, but also has dd, the result will be a diluted black, or a blue rabbit! Likewise, if the rabbit has both bb and dd, it would be diluted chocolate, or a Lilac! So, to review;
Black: BBDD, BbDD, BBDd, or BbDd
Blue: BBdd or Bbdd
Chocolate: bbDD or bbDd
Lilac: bbdd (always, no matter what!)
Quick Review - Assume the following:
B = Black Pigment gene
b = Chocolate Pigment gene
(B is always dominant to b)
D = Dominant Pigment gene
d - Dilute Pigment gene
(D is always dominant to d)
Black rabbits must have at least one "B" and one "D" to produce the dominant black pigment and can have one of the following color combinations:
i) BBDD (genetically pure black, will only produce blacks)
ii) BBDd (carries a dilute gene, able to produce a blue)
iii) BbDD (carries a chocolate gene, able to produce blacks and chocolates)
iv) BbDd (carries both a chocolate gene and a dilute gene, able to produce all four colors)
Blue rabbits must have at least one "B" gene and double "dd" genes to produce the dilute factor. They can have the following genetic combinations:
i) BBdd (A blue with only black genes)
ii) Bbdd (A blue with black and chocolate genes)
Chocolate rabbits must have double "bb" genes and at least one "D" gene in order to exhibit the chocolate pigment. They can have the following genetic combinations:
i) bbDD (A genetically pure chocolate with no dilute genes, able to produce chocolates and blacks)
ii) bbDd (A chocolate with a dilute gene, able to produce chocolates and lilacs if mated to another chocolate, lilac or blue and all four colors if mated to a black)
Lilac rabbits must have double "bb" genes and double "dd" gene in order to exhibit the chocolate pigment. They can only have the following genetic combination:
i) bbdd (able to produce all four colors if mated to a black, 3 colors if mated to a chocolate 2 colors if mated to a blue and only lilacs if mated to a lilac).
Solving Genetic Probability I
Solving the probability of various genetic combinations, which creates the four colors is quite simple. If you know how! In this article, I will show how to follow a cross, using only one gene at a time. This simple cross can be done with Black (BB or Bb) and Chocolate (bb) or Black (DD) and Blue (dd). It would still be possible to get other colors out of these crosses, but it takes a more complicated process to be explained next time. The first step in solving genetic probability is to make a box, and then draw a tic-tac-toe board inside, which is called a Punnett Square:Now, you are going to write your dam’s genotype (I’m going to use BB for an example, which is black) across the top, and your buck’s genotype (bb which is chocolate) down the left side.
| B | B | |
| b | ||
| b |
| B | B | |
| b | B | B |
| b | B | B |
| B | B | |
| b | B b | B b |
| b | B b | B b |
So, if you look back at the last page (or just remember, or just keep reading and trust I know what I'm talking about) , Bb is black, so if you breed a BB Black to a bb Chocolate, you will get all blacks. Then, what would happen if you bred two of the offspring from this cross? Follow the directions from above, and you will find that you will get 75% Black, and 25% blues.
| B | B | Genotype: 100% Black Phenotype 100% Black |
|
| b | Bb | Bb | |
| b | Bb | Bb |
This process can be used with Blue and Black, using the same process, but replacing the B’s with D’s or d’s. Here is an example with a Blue (dd) doe and a Black (Dd) buck;
| D | d | Genotype: 50% Dd 50% dd Phenotype: 50% Black 50% Blue |
|
| d | Dd | dd | |
| d | Dd | dd |
Solving Genetic Probability II
We have worked with black to blue, and black to chocolate, but what about blue to chocolate, and all of the lilac crosses (lilac x black, lilac x blue etc.)? The answer is using a more complex Punnett square. A simple cross to begin with is a homozygous black (BBDD) doe and a Lilac (bbdd) buck. It is possible for theblack to pass on any combination of the following (note: using the superscript helps to keep track of which gene is which).
B1B2D1D2
Combinations: B1D1,B2D2,B2D1,B2D2
So, write down each of these combinations across the top (without superscripts to avoid confusion),
| BD | BD | BD | BD | |
The buck's genes are going to be very similar (b1b2d1d2).
Combinations: b1d1,b2d2,b2d1,b2d2
Write down each of these combinations down the side (once again without superscripts),
| BD | BD | BD | BD | |
| bd | ||||
| bd | ||||
| bd | ||||
| bd |
Now, just like before, take each gene, and pass it on to each of the offspring.
| BD | BD | BD | BD | |
| bd | B | B | B | B |
| bd | B | B | B | B |
| bd | B | B | B | B |
| bd | B | B | B | B |
Next, do the buck's black genes so that there isn't any confusion! (remember that dominant genes go first: BB, Bb, or bb, not bB, however writing two separate genes, such as dB is possible if the first is dilute, and the second isn't).
| BD | BD | BD | BD | |
| bd | Bb | Bb | Bb | Bb |
| bd | Bb | Bb | Bb | Bb |
| bd | Bb | Bb | Bb | Bb |
| bd | Bb | Bb | Bb | Bb |
Now, put the doe's dilute genes down (because she is homozygous, all genes will be D).
| BD | BD | BD | BD | |
| bd | BbD | BbD | BbD | BbD |
| bd | BbD | BbD | BbD | BbD |
| bd | BbD | BbD | BbD | BbD |
| bd | BbD | BbD | BbD | BbD |
Now, write each of the buck's dilute genes.
| BD | BD | BD | BD | |
| bd | BbDd | BbDd | BbDd | BbDd |
| bd | BbDd | BbDd | BbDd | BbDd |
| bd | BbDd | BbDd | BbDd | BbDd |
| bd | BbDd | BbDd | BbDd | BbDd |
Now all that is needed to be done is to figure out the phenotype and genotype, which for this particular situation is easy! Just follow the exact same process as is written above, finding the Genotype first, then using that to find the Phenotype.
| BD | BD | BD | BD | Genotype: 100% BdDd Phenotype: 100% Black |
|
| bd | BbDd | BbDd | BbDd | BbDd | |
| bd | BbDd | BbDd | BbDd | BbDd | |
| bd | BbDd | BbDd | BbDd | BbDd | |
| bd | BbDd | BbDd | BbDd | BbDd |
Currently Missing a Page Here - A Gene
The C Gene
The C or colour series is a bit more complicated, because certain heterozygous paired genes show a difference than a homozygous pair. The full colour gene represented by C is dominant to all other genes, and leaves all other genes the same, altering nothing. So if you have C paired with any other C gene, the rabbit will be self whatever color the other genes make it.
The gene dominant to all genes except the C is the C chd This is the Dark Chinchilla gene . When the C chd is paired with the agouti gene, the result is a chinchilla rabbit. This is also known as Light Grey in Flemish. When mixed with the B and D genes, it creates a Chocolate, Blue, or Lilac Chinchilla, which is showable in some breeds (Holland Lop, English, French, and Satin Angora), but not in others (Netherland Dwarf, Satin). It is this gene that makes the the beautiful color of the chinchilla breeds, American Chinchilla (pictured below), Standard Chinchilla, and Giant Chinchilla.
So how does the Cchd make an agouti become chinchilla? It actually removes the red pigments from the coat genetically. If you think about the red color in an agouti, then replace the red with grey, you have a chinchilla. This gene is what makes a Gold Steel, Silver Steel (take the red/gold out of a gold steel and you're left with silver!), it also causes the difference between Magpie and Japanese Harlequins (take the red out of a Japanese and you're left with the main color and white: Magpie!). It is also the C chd gene that causes the difference between a Otter and a Silver Marten. A Otter without red is indeed white, or Silver Marten!
The Cchlgene is misleadingly named the light chinchilla gene. However the effect is not that of a chinchilla, or anything similar, but is that of a shaded rabbit. The ears, saddle, nose, feet, and tail are all darker, and become lighter in all the other areas. There is no distinct point where the colour gets lighter; it should be just a gradual in a well-colored animal. The Siamese Sable (aa B? C chl ? D?) is one variety that shows the light chinchilla gene. Other varieties that have the C chl gene are the Siamese Smoke Pearl (aa B? Cchl? dd).
When this gene is paired with the Tan gene, it results in a Sable Marten, because it successfully removes both the red from the fur, and causes the coat to become Sable. Similarly, Cchl is paired with both the tan gene and the dilute gene, the result is a smoke pearl marten (pictured below is a Jersey Wooly smoke pearl marten).
When a rabbit is heterozygous with the Cchl and either ch or c the effect is the same, however it is lighter than a homozygous C chlCchl is.
The pointed white or ch gene is similar, but when it is homozygous, it results in a pseudo-albino otherwise known as a pointed white, Himalayan, or Californian. What this gene does is removes ALL pigmentation from all areas, but allows pigmentation to gather in the coldest areas. Thus causing a white rabbit with colored extremities (nose, tail, feet, and ears). Once again, not fully dominant, when it is paired with a c, the colored points become lighter. The color that shows through is the color described by the other genes, however only the four brown/dilute genes show, for some reason the agouti and other genes are masked. So it is impossible to have an agouti Himalayan.
If the last gene, c is combined with a ch, the result is a lightly marked animal.
If a rabbit has two c genes, the result will be a completely white animal with red eyes (Albino) . Although the other genes for other colors are still there (and will show up in the next generation if not bred white to white), they are masked by the albino gene. For this reason, a white rabbit is not genetically self, but could be anything.
The "E" Gene
The next gene is the E gene, which alter a few different things, depending on which gene is passed on. The first, and most dominant gene is Es which creates a false steel, or all black rabbit. If Es is combined with an E gene, it produces a steel rabbit. Steel is the base colour combined with either gold, or silver-tipped hairs. The effect of the heterozygous EsE is that it removes the red from the coat by extending black down the tip of the hair in an agouti rabbit. So where the chinchilla gene (Cchd) replaces the red with grey, the steel gene actually just covers up the intermediate band, leaving the tip of the hair red (gold steel).
Homozygous EE leaves the colour the same as before. All self colored rabbits have at least one E gene.
The Ej is next, and it creates a Harlequin colored rabbit. Harlequin is a colour in a pattern resembling either a checkerboard, or a set of strips around the body. It is created by randomly removing the red from some portions and removing the black from the others, leaving patches of black and patches of red. In the event that this is combined with a chinchilla gene, the result is a Magpie harlequin (black and white). In combination with the b and d genes, the result is either red or white in combination with black, blue, chocolate, or lilac.
The last, and completely recessive gene is the e gene, or the non-extension gene. It is the gene that removes the black in an agouti. So, in an agouti, it makes a red/orange, while in a self, it creates tort. If a rabbit is an agouti with both the chinchilla and non-extension genes (AA ?? cchd? ?? ee> the result is an all "frosty" rabbit because the chinchilla gene removes the red, and the non-extension removes the black. The rabbit would have brown (or blue) eyes and would be a frosty pearl, which is beautiful!
The En Gene
The broken gene is a little more difficult to understand, because it is incompletely dominant. The broken gene is En. I am going to start with the recessive gene, rather than the dominant one, because it is slightly easier to understand. When a homozygous en is present, the result is a solid colored rabbit. Nothing is changed from self.
When heterozygous Enen, the result is a broken rabbit, or a rabbit that has any colour in conjunction with white. Below is a photo of a pair of young broken Satin does.
The degree of "brokeness" is determined by modifiers. As is where the markings are, note that the broken on the left has a full butterfly, while the one on the right has only half of a butterfly, that is a result of modifiers, which I will get to later. The English Spot, Checkered Giant, and Rhinelander are all breeds that are actually broken, but have been specifically bred to result in exact markings.
Brokens
A homozygous EnEn results in a rabbit that has marking that are referred to as "charlie." A charlie usually has colored ears, light nose markings, and light markings over the back and side. These differ from Broken, as there is not near as much colour on the rabbit. Surprisingly, the Hotot and Dwarf Hotot are actually both charlies bred specifically for no markings with the exception of a eye circle. Breed a Hotot/Dwarf Hotot with a solid color rabbit, and you will get all broken!
Charlies
** Broken and Charlie photos come from Rabbit Production Sixth Edition. Cheeke, Lukefahr, Patton, McNitt. The Interstate Printers and Publishers, Inc.Danville, IL. 1982.
Modifiers
What on earth is a modifier? A modifier is what modifies (for lack of a better word) the color of the rabbit without having a specific representative gene. Basically it is what makes the color of a tan vary, or the shade of red, or the deepness of the surface color. These are modifiers because they do not specifically change a color, like a bb makes black become chocolate. Rather many genes work together to modify the coat color of the rabbit. These modifiers alter the red, many modifiers give you a deep red, while few give you a light red, or sometimes orange. Modifiers also have an effect on brokens, giving the various patterns. It also is what affects the pattern of a harlequin. To a degree it can alter the shade of self coat colours. It is the modifiers that alter the depth of the surface color, which makes it seem darker or lighter. These modifiers play a HUGE part of the color of the rabbit, but there is not a lot of information on them!
Hey, you are now a rabbit coat color genetic expert! Congratulations!
