Genetics of rabbits cover many things such as breed, coat colours, size, shape, eye colour etc etc.
Most rabbit breeders are very clued up when it comes to genetics. The better the understanding of genetics, then the better the breeder.
Breeders usually associate the word 'genetics' to the determining factors that make up the overall colour of a rabbit. (That's rabbit 'color' to our American friends).
However there are other factors that are important when you are looking at the genetics of rabbits, like the dwarf gene, the albino gene and what dictates life-span and even the behaviour in different species.
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Rabbit colours are part of rabbit genetics and can, of course, be genetically modified. The jury is still out on this one as far as I'm concerned. I can't really see an immediate benefit to messing around with them to this extent.
Read the story on luminous rabbits glow in the dark rabbits and you can make up your own mind.
However the natural rabbit genetics that affect coat colours, textures, length of fur etc is rather a complex but fascinating subject. I'm not a
great mathematics lover at the best of times and initially I looked at all the complicated codes and formulas and just about had a brain melt-down. So I have called on a lot of help
to put the following information together and to make it as easy to understand as
Rabbit genetics are all about genes of course and these are on individual points (loci), on a chromosome, which are strings of DNA.
A gene determines the appearance or function of a body part. This gene may act alone or with other genes to determine a particular appearance or function.
Chromosomes and the genes on them pair up in most cells. There are 22 pairs of chromosomes in each cell of a rabbit, (except in the red blood cells and the sex cells).
The same location on each chromosome of the pair controls the same characteristic. There are thus two genes involved - one on each chromosome at the same location.
A particular gene location may allow only one type of gene to be present there; whereas, another location may allow different types of genes to occupy it.
Those locations that allow
only one type of gene on both chromosomes do so because any other type
would cause either harmful or fatal effects. An example of bad rabbit genetics at work would be in the genes that control the shape of the teeth and if any other
than the expected gene type is present at this location, the teeth would
not grow in right, which could cause starvation with the inability to take in food properly.
Some locations allow different types of genes to stay there, causing different expressions of the same characteristic without deleterious effects. For instance, a hair colour gene location may allow 2 genes of different types to occupy that location. One type of gene may be the gene that produces black hair, the other brown. Each chromosome may house either the black or the brown gene.
Some of the genes match their counterparts on the other chromosome exactly and some do not. When two genes match, such as, two black genes, this is called a homozygous pairing (homo- meaning the same). When the genes are not the same, such as one black and one brown gene, this is called heterozygous pairing (hetero- meaning different). Another name for heterozygous is hybrid.
When we speak of a gene location, we're really talking about two points - one on chromosome A and one on its companion chromosome B. Since there are two chromosomes involved, there are two genes involved - one from each chromosome. The points on each chromosome match up perfectly with the points on its companion chromosome.
Thus, a location is made up of two genes.
In rabbit genetics, when two different genes occupy the same location, one of the genes expresses itself in the characteristic and the other either doesn't or does so to a lesser extent, modifying the effects of the other gene.
When one gene expresses itself more than the other, it is called the dominant gene. The other gene is called the recessive gene.
When the dominant gene expresses itself completely, to the exclusion of the recessive gene, this is called complete dominance.
Most dominant genes
express themselves completely. When the recessive gene modifies the
expression of the dominant gene in some way, the relationship of the
dominant gene to the recessive gene is called incomplete dominance.
When a buck produces sperm or a doe produces eggs (both of these cell types are called gametes), the chromosome pairs in the cells that create these gametes divide, putting one chromosome of each type into the gamete.
When the doe's egg is fertilized by the buck's sperm, the chromosome from the sperm unites with the same chromosome type in the egg and the chromosome pairing is once again restored.
Whatever genes that came from the buck are now matched up with the genes of the doe. The expression of these genes in the resulting offspring depends on their dominance and how the other genes relate to each other.
The determination of rabbit genetics is based on the law of probability. Without getting into the complicated aspects of gene mapping distance and linkage, here is a simple concept of how you can figure what your offspring will look like.
In rabbit genetics it is common to represent a dominant gene by a capital letter and its recessive counterpart(s) as lower case.
Let's take the black/brown colour location. This location is called B. The black gene, which is completely dominant, is represented as 'B'. The only known recessive gene that can occupy this location is brown, represented as 'b'. Since a location has two genes, there are 4 possibilities at this location:
BB, bb, Bb, bB.
Since black is completely dominant, if you have a rabbit that has at least one B at this location, the rabbit will have black in its fur. Thus, rabbits having the combination of genes: BB, Bb, or bB will have black in its fur. Rabbits having the combination of bb will have brown.
Note that it usually requires both recessive genes (bb) at a location for that set of genes to express itself. When the dominant gene is not completely dominant, the recessive gene will modify the expression of the dominant gene in some way. As far as the black/brown location, the black gene is completely dominant and will always express itself, if present, to the exclusion of the brown gene.
There are other genes that work with the B gene to determine that actual colour of the rabbit. We will assume in this discussion that the other genes are set up to produce a solid black or a solid brown rabbit.
Let's take a black rabbit and mate it with another black rabbit. What are the possible offspring? We know that a black rabbit has at least one B gene. If we don't know for sure the other gene is B or b, we can represent that other gene as '_' (unknown). We can thus represent both genes in the black rabbit as: B_.
When it comes to dominant genes, we usually cannot know for absolute certainty that the other gene of the pair is also the same dominant gene. The exception to this is when the recessive gene acts with the dominant gene to produce a certain known characteristic, such as English spotting.
Getting back to our example, we have one black rabbit whose black/brown gene location is represented as B_. Let's assume the other black rabbit we are mating it to is also B_.
Breeding the rabbits [B_ x B_], we combine the left gene of #1 with the left gene of #2 , giving BB - a black rabbit.
Then we combine the left gene of #1 with the right gene of #2, giving B_ - another black rabbit.
Then we combine the right gene of #1 with the left gene of #2, giving _B - another black rabbit.
Then we combine the right gene of #1 with the right gene of #2, giving _ _ -unknown. We thus have:
B_ x B_ = (BB, B_, _B, _ _)
Let's fill in the blanks. If one of the rabbits had both black genes (BB) all of the litter would be black, without exception, even if the other rabbit had one brown gene. It wouldn't matter how many times you bred these two rabbits together, you would always have black offspring.
BB x B_ = (BB, B_, BB, B_)
Remember, if at least one black gene is present, the rabbit will be black.
Only if both rabbits had one brown gene would a brown rabbit (bb) be produced. It may take two or more breedings to see a brown rabbit because the probability is only 25%.
Bb x Bb = (BB, Bb, bB, bb)
How can we test to see if one of the black rabbits has a brown gene in it? Simply mate the black rabbit with a brown rabbit. If you get any offspring that are brown, you know for a fact that the black rabbit has a brown gene in it. The probability is that you should get about 50% brown offspring. Here is the formula:
B_ x bb = (Bb, Bb, _b, _b)
Filling the blanks, if the unknown gene is B, all of the litter will be black. If the unknown gene is b, about half should be brown.
Since we are talking about probability here, the litter could still be all black or could be all brown.
If you get an all black litter, you may still have to breed one or more times to see if at least one brown rabbit is produced.
If a brown rabbit is produced, you know for a certainty that the black rabbit has one black gene and one brown gene.
If you get all black rabbits from matings all the time, it is probable, but not certain, that the black rabbit has both of its genes black.
In summary, to test for the presence of a recessive gene when only the dominant is showing, mate it with a rabbit that shows the recessive gene. If at least one of the offspring shows that recessive gene, you know positively that the rabbit you were testing has the recessive gene along with the dominant gene.
If you do not get any offspring showing the recessive trait after several litters, the odds are that the rabbit in question does not have the recessive gene (but you can never know with absolute certainty).
Remember that about half of the offspring should show the recessive trait. But if no rabbits in the litter expresses the recessive gene, we're still talking probabilities here.
The failure of the recessive gene showing up in all of the litters does not prove the tested rabbit does not have the recessive gene, just that the probability of its having it is low.
But if any rabbits in the litter show the recessive gene, it is proof positive that the tested rabbit has the recessive gene along with the dominant in it's rabbit genetics.
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