Practical Colour and Coat Length Genetics for Abyssinian
& Somali Breeders
The article below was written by George Kennedy and is reprinted from The Abyssinian Breeder magazine
It is apparent that a significant minority of the subscribers to this magazine does not have a clear understanding of how Abyssinians (and Somalis) inherit coat colour or length. This is evidenced by the number of impossible and improbable claims made in submissions to the Guide to Breeding Abyssinians - I have to "filter" these to ensure that other readers are not misled. Again, there is unprecedented interest in breeding dilute Abys and Somalis, and for me, a frequent need to explain to callers that what they propose is either downright impossible or else it has only a tiny chance of succeeding. This article is therefore provided for the many subscribers who seem to need it. It is devoted to the four basic, eumelanistic Abyssinian colours and two coat lengths. For readers on the far side of the Pacific, Tawny = Ruddy and Cinnamon = Red
Abyssinians - and indeed all mammals - are what they are because of their genetic make-up. At conception, a sperm from the father fuses with an egg from the mother, and the eventual result is a cat, created because a large number of genes from each parent (as many as 3000. I heard someone say), each carrying a lot of specific information, are combined as a result of the fusion. Some of the genes determine the number and shape of paws, other determine the sex, and so on. In this article, I want to talk about the genes that determine the colour and coat length.
First, it is essential to define a few basic terms.
Genotype the genetic make-up of the cat, for colour and coat length, e.g.: Cinnamon Somali capable of producing Blues or Blue Aby capable of producing Cinnamons (must be suitably mated in each case).
Dominant the dominating or fallback characteristic, to which cats revert unless conditions are suitable for something else (come back to this point - the definitions of this term and the next four are inter-locking, and it helps to re-read). In this context, the dominants are Tawny and shorthair. It is thus quite likely that mating a Cinnamon Somali to a Blue Abyssinian could result in nothing but Tawny Abyssinians, but see below.
Homozygous not capable of producing any coat colour or length other than its own (and the dominant of course anyone can produce the dominant), i.e., not "carrying" anything (see below). If you think about it, you will notice that a homozygous cat is one whose genotype is the same as the phenotype.
Carrying an Aby/Somali is said to be carrying a colour or coat length when it is capable of producing offspring of a colour or coat length different from its own and the dominant. A Tawny Aby could carry Cinnamon, or a Blue Aby could carry Somali. However, no-one could carry Tawny and no Somali could carry Abyssinian, because those are the dominants.
Heterozygous the opposite of homozygous; refers to a cat carrying a colour or coat length.
Recessive this is a gene over which the dominant dominates. For instance, mating a homozygous Tawny Aby to a homozygous Cinnamon Aby will result in all the offspring being Tawny: Clearly Tawny dominates over Cinnamon. The recessive genes governing coat colour and length are Cinnamon, Blue and Somali. Fawn is a combination of Blue and Cinnamon. There is no partial dominance, so Blue does not dominate over Cinnamon (or vice versa), and neither of them dominates over Somali (and vice versa). Again, there is no sex linkage, as there is with certain Tabby colours. This means that males and females can have all colours and both coat lengths with equal probability. A most important thing to remember is that kittens of recessive colour or coat length are possible only if both parents are capable of producing them. For instance you can get (some) Somali kittens only if each parent is either a Somali or Somali carrier. This will become clearer as the article progresses, I hope.
'Well, that was very interesting." I hear you cry, "but lets get down to tin tacks: How do I breed Fawn Somalis?!" "With some difficulty," I have to answer, "and if you dont already know, you might as well read the rest of this article."Some Basic Genetics
The genotype of a homozygous Tawny Abyssinian is commonly written AABBDDTaLL The AA stands for the basic agouti (yellowish-grey) background colour and ticking - it does not vary from one Aby colour to another. BB stands for black pigmentation. It becomes bb (brown) in a Havana or Burmese, and blbl (light brown) in the Cinnamon Aby or Somali.
The B, b and bl are associated with each other, and a series such closely associated genes are known as alleles The genotype of the Cinnamon Aby is thus the same as for the Tawny, except that BB is replaced by blbl. For a Tawny carrying Cinnamon, the BB is replaced by Bbl in our standard notation.
DD stands for dense pigmentation, and becomes diluted (and written dd) in the Blue Aby; the notation for a Blue carrier is Dd. Fawn is a combination of Cinnamon and Blue, and hence the genotype of the Fawn Aby is written AAblblddTaLL.
Ta is the Abyssinian tabby coat pattern, being a reduced form of tabby occurring on the face and head but (ideally!) not on the chest, limbs and tail. It is dominant over the other two tabby alleles: T, the mackerel tabby, and Tb the blotched tabby.
Finally, LL means that the cat is shorthaired and homozygous: the genotype of a Somali carrier has Ll and a Somali has ll. Consequently, the genotype of a Tawny Aby carrying Cinnamon, Blue and Somali is AABblDdTaLl.Breeding Colour Recessives and Somalis
Cells unite at random during the conception process. Thus, close to half of all the kittens ever bred are male and half are female, but there is no rule that says "the last kitten born in this litter was male therefore the next one will be female". The same applies to the genes governing colour inheritance. So if a particular mating is equally likely to produce Blues as Tawnys, you will not get two of each in every litter of four, and it is quite on the cards that you will get the occasional all-Tawny or all-Blue litter. What it does mean is that. if such a mating is performed a large number of times (e.g., 20 or more), then on average half the kittens will be of each colour. It is important to remember that statistical averages are not prescriptions for individual litters.
An excellent aid to working out what happens when cats of given genotypes are mated is the "checkerboard" diagram drawn up for that mating, like the one below showing what happens when a Tawny carrying Cinnamon is mated to another Tawny carrying Cinnamon. Note that only the variables are shown for simplicity: Clearly, each cat will have AA, DD, Ta and LL in its genotype.
Genes from Tawny carrying Cinnamon [Bbl]
Each of these intersections is as probable as any other, and so the checkerboard diagram shows the (statistical average) gene pairings. You can see that from a mating like this, 25% of the kittens would be homozygous Tawny (BB), 50% would be Tawny carrying Cinnamon (Bbl) and 25% would be Cinnamon (blbl). The important conclusions are that some kittens are Cinnamon, most of the kittens (75%) are Tawny, and most but not all of the Tawny kittens will carry Cinnamon. Moreover, because Tawny is dominant, the Cinnamon carriers will look Tawny and you will not be able to tell them apart from homozygous Tawnys.
Feeling brave? If you are, lets try to see what can happen when a Tawny Aby carrying Blue and Somali is mated to a Tawny Somali carrying Blue.
Genes from Tawny Aby carrying Blue and Somali [DdLl]
DL Dl dL dl
Tawny Somali Dl DDLl DDll DdLl Ddll
[Ddll] dl DdLl Ddll ddLl ddll
Dl DDLl DDll DdLl Ddll
dl DdLl Ddll ddLl ddll
Adding up the results, we get 1/8 DDLl (Tawny Aby carrying Somali), 1/8 DDll (Tawny Somali), 2/8 DdLl (Tawny Aby carrying Blue and Somali), 2/8 Ddll Tawny Somali carrying Blue), 1/8 ddLl (Blue Aby carrying Somali), 1/8 ddll (Blue Somali). So, what have we learned in general?
Once more with feeling: What do you get when you mate a Cinnamon Aby carrying Blue to a Blue Aby carrying Cinnamon?
Genes from Blue Aby carrying Cinnamon [Bbldd]
This mating, on average, produces 1/4 BblDd (Tawny carrying Cinnamon and Blue), ¼ Bbldd (Blue carrying Cinnamon), ¼ blblDd (Cinnamon carrying Blue), and ¼ blbldd ("Blue and Cinnamon", i.e., Fawn). This mating represents one of the two best chances of getting a rainbow litter, but dont expect one the first time you try! The other mating giving exactly the same result (on average) is Tawny carrying both to Fawn.
We could go on like this, but there are 9 possible Aby genotypes: Tawny, Tawny carrying one colour, Tawny carrying the other, Tawny carrying both, Cinnamon, Cinnamon carrying Blue, Blue, Blue carrying Cinnamon,and Fawn; this results in 45 different combinations (not 9² = 81 because there are duplications). Dealing with each in detail would fill the magazine. Moreover, if Somalis are added, we get 27 genotypes (the 9 above, plus the same 9 carrying Somali, plus the same 9 being Somali) and the total number of combinations becomes 378. Just the same, I once worked out what you get when mating two Tawny Abys carrying Cinnamon, Blue and Somali. It took an 8 X 8 checkerboard, and as expected, you get (on average) all 27 varieties, including a 1 in 64 chance of breeding a Fawn Somali. The table below is a reprint from an earlier article of mine and gives the results in a nutshell.
AVERAGE LITTER EXPECTATIONS FROM ABYSSINIAN MATINGS
If you want to know what to expect from a litter involving Somalis or Somali carriers that are or carry Cinnamon or Blue, just substitute Somali for the missing colour in the Average Litter Expectations table. So, if you happen to be interested in Somalis and Blues, substitute Somali for Cinnamon in the table, and just remember that where blbldd gave a Fawn Aby, the ddll combination represents the Blue Somali. A table including Cinnamon, Blue and Somali is too large for inclusion, but most of the results can be extrapolated from the table provided.
Does My Cat Carry XYZ?
No, if it is alreadyXYZ - thus a Blue Aby does not carry Blue (neither does a Fawn carry Cinnamon or Blue. because it represents a combination of both). No, if XYZ is Tawny or shorthair, because those are dominants and all Abys/Somalis can produce them if suitably mated. No, if neither parent is or carries XYZ, except for one-in-a-million mutations like the Scottish Fold or Cornish Rex. Yes, has one XYZ parent. Yes, if It has produced at least one XYZ kitten. Maybe, if neither parent is XYZ but one or both parents carry XYZ.
If the answer is "maybe", you can find the chances of that "maybe" by looking up the preceding table. For example, if both your cats parents are Tawny carrying Cinnamon, your cats chances of being a Cinnamon carrier are 2 out of 3 (think about it: 25% of offspring on average are Cinnamon while 75% are Tawny; 50% carry Cinnamon, so your cats chances are 50/75 = 2/3). On the other hand, if you mate a Tawny carrying Blue to one carrying both Blue and Cinnamon, and your kitten is Blue, its chances of being a Cinnamon carrier are 1/2 (12½ divided by 12½ + 12½). However, cats that carry do not normally look different from cats that dont, and thus the only way to be sure is to prove it by getting your cat to produceXYZ kittens.
Proving That a Cat Carries (or Does Not Carry)XYZ
There are really two aspects to this question:
The first one is easy. Test mate your cat to an "XYZ cat", i.e., to a Cinnamon (or Fawn) when testing for Cinnamon, to a Blue (or Fawn) when testing for Blue, to a Somali when testing for Somali. Wherever you look in the earlier table, you can see that you have twice the chance of breeding XYZ when one of the cats is XYZ and the other is a carrier than if both are carriers. The other important thing is that if you are testing for a lot of things, you should test one after the other; that is really faster than trying to test for everything at once, unless you get lucky. Thus, if you hope your Tawny cat may carry Blue and Cinnamon, it will be faster to prove that if you mate it to a Cinnamon and next time to a Blue, than to a Tawny carrying both. Those of you who catch on fast (i.e., the vast majority of subscribers), will have already worked out that the best sort of "test cat" is a Fawn Somali.
Let us now look at the second question. You've mated your Tawny female which you hope carries Cinnamon to a Tawny that definitely carries Cinnamon (you had no access to a Cinnamon stud), and all four kittens in the litter are Tawny. On average, a quarter of them should be Cinnamon - does that mean that your cat doesnt carry? As it happens, the answer is no - your cat could still carry, and indeed the chances of there being no Cinnamon kittens in a quartet from such a mating are nearly 32%. That is, your cat still has a 32% chance of being a carrier.
The laws governing this sort of thing are the laws of chance - laws that could answer a question like "what are the chances of getting tails seven times in a row when fairly tossing an unbiased coin"? Accordingly, the formulae tend to be complicated, and all I propose to do here is to give you a table that covers most of the eventualities. The table is drawn up for Tawny carrying X (Tx) mated to X or Tx. but it would work in exactly the same way for (say) a Cinnamon carrying Blue, or a Blue carrying Somali.
Percentage Odds for an "X" Kitten in a Given Litter
Rather interesting, isnt it? For example, you can now work out how "odds-defying" some of your litters have been. More importantly, you can calculate your cats chances of being a carrier of "X", where X is of course equally applicable to Cinnamon, Blue or Somali. Statistically, an event can be discounted if its probability falls below 1%. Thus, even getting no Blue kittens in a litter of 6 in a Blue X "maybe Blue carrier" mating, does not quite put paid to a cats chances of being a carrier. However, a second - even small - litter without Blues to a Blue would mean you should give up on this cat.
May the odds be with you!
This page was last updated on 11-Feb-09
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