What is Rufus Factor, and How does it work?
Stephen Roush, ARBA Judge #475
There has never been a comprehensive description of the rufus factor as it applies to the color effect on domestic rabbits. That is because there are many theories and guesses, but not any real confirmation based upon quantifiable data. The following is an attempt to take what I have come to feel is the most credible theory, and to expound on how it applies. This is based upon experience with developing the Tan Mini Rex color, which requires a deep rufus color to be correct. It also requires a wideband gene, and since the wideband gene has been associated with rufus, at least by many past writers and theorists, a few comments about that gene are also in order.
First, what is the rufus effect? It is some type of a gene impact that in the ideal sense, will create a brilliant deep rich red/rust shade of a tan or chestnut shade. The term ‘gene modifier’ is often used to explain that this is not a separate gene pair, but is a gene effect..
I actually see NO reason to not accept that the action that causes the phenotypic deep mahogany, Rust red color is indeed a gene, but rather than a single gene, I suggest it is a gene series, which interact to result in the color.
Mini Rex breeders should wonder why this article is showing up for the first time in the Mini Rex News. The rationale is that, first, that is a breed I enjoy, and have experimented with. The more important justification is that the Castor mini Rex is undoubtedly the most shown color variety of the breed. Even the broken variety has more Castor broken than any other combination. The reason for castor being so prevalent is that the genetic combination of A_B_C_D_E_ that results in castor consists of all dominant genes. Thus, it is the default color that usually arises when crosses are made between animals of different colors. An example is a recent question on a Mini Rex chat room asking what would be the outcome of crossing a Fawn colored rabbit to a Chocolate. The answer is clearly, 100% Castor. Many other examples can be made of this fact.
Rufus factor affects the overall color of the Castor, and it’s non-extension sibling, the Red, more than any ‘currently accepted’ Mini Rex variety in 2006. The band color affects the Rich Chestnut brown that is required of the color. The band is where the deep rust color comes from. As type becomes more and more uniform, a true differentiator of the animals will be their color. Reds have emerged in the last few years as a true challenge for breeders as they strive to make the color more representative of the red New Zealand and Thrianta colors. The washed out orange looking reds will soon be a thing of the past.
A critical impact to achieve the goals of better color and better uniformity of color is the rufus gene. Understanding it, and how it works, can vastly improve color that needs to be richer and deeper.
The wide band gene has been often linked with the rufus gene. This is understandable, as the wideband gene allows the rufus effect to be more visible, and to look deeper and richer. However, any breeder who has experimented with the wideband gene will readily explain that there is no guarantee of deeper color just by having the wideband effect. Wideband effect is seen primarily in the Tan Rabbit breed, the Thianta breed and the Belgian Hare breed. I surmise that it is also part of the genetics of the New Zealand red, but have no evidence or experience to assure you that is true. These very rich colored breeds rarely have much departure from the deep rufus color effect, unless you breed away from them. Some think that the fact that the loss of wideband (ww) cause this loss of color. However, my research has shown that crossing a true Tan rabbit to a solid rabbit will yield tan pattern offspring that still have a relatively dark belly color BUT are not wideband..as there is undercolor on the belly.
The challenge is to recombine the wideband while still retaining the rufus factor. This is complex and very difficult. This article will explain why that is so. Wideband is a simple dominant/recessive gene. Even the wideband effect is not shown on self (aa) rabbits if the rabbit carries the double recessive (ww).
Rufus, and How it possibly works
It does seem, from all accounts over many years, that rufus coloration is the result of an additive effect. The more (or less) of some type of genetic ‘color trigger’ will cumulatively result if the deeper or lighter ‘tan/red’ of the visible color. Taking this as an accepted premise (and I’ll ask you to accept a few other conceptual mechanisms in the following text), the theory then comes down to how many elements are involved, and how do they work?
Assume a parent rabbit has six (6) genetic ‘rufus markers’ that translate into the reddish appearance in their phenotype. If you accept this premise, then it becomes a simple matter of reproductive genetics that the parent can only transmit half of these to the offspring. This is because the offspring can only end up with 6 ‘markers’, and that means only three can come from each (of the two) parents.
Each ‘marker’ can then be labeled as either positive modifier (more rufus) or a negative modifier (less rufus). The more positives that are present means the color is a darker red, and the more negatives that are present means the color is a lighter red.
The six markers can be arrayed into seven possible combinations. They would be:
Table #1
DESCRIPTOR/ SHADE Marker configuration
Very Light/ Wheaten - - - - - -
Light/ Honey + - - - - -
Light Medium/ Fawn + + - - - -
Medium/ Tan + + + - - -
Medium dark/ Copper + + + + - -
Dark/ Russet + + + + + -
Very Dark/ Mahogany + + + + + +
However, the reproductive contribution from each parent for rufus can only consist of three gene markers, and these contributions will vary in their potential to influence the rabbits color intensity also. These three gene markers can only be arrayed in four possible combinations from each parent, and even those possible combinations are dependent on what the parent can contribute, based upon what gene markers that they have inherited and thus carry.
The only four possible combinations are:
Table # 2
DESCRIPTOR Marker Configuration-
Very Light - - -
Light + - -
Medium + + -
Dark + + +
When the ‘three gene marker’ configuration from one parent combines with the ‘three gene marker’ configuration from the other parent, the resulting rufus effect on the color (of the offspring) is the combination of the six gene markers. These various combinations will result in the total range of ‘rufus factor’ in the phenotype. Those total pairings are listed in Table # 3.
Table #3
Parent #1
Parent #2
- - -
Very Light - - - - - -
Very Light + - - - - -
Light + + - - - -
Light Medium + + + - - -
Medium
+ - -
Light + - - - - -
Light + + - - - -
Light Medium + + + - - -
Medium + + + + - -
Medium Dark
+ + -
Medium + + - - - -
Light Medium + + + - - -
Medium +++++ -
Dark +++++ -
Dark
+ + +
Dark + + + - - -
Medium + + + + - -
Medium Dark +++++ -
Dark ++++++
Very Dark
Each ‘ six marker’ rufus phenotype can provide to each breeding only so many unique ‘three gene marker’ combinations as possible contributors toward the eventual rufus phenotype of the offspring. These possible combinations are listed in Table #4.
Table #4
Descriptor/Shade Possible ‘3 gene marker’ Breeding Sets
Very Light/ Wheaten 100% Very Light (- - -)
Light/ Honey 50% Very Light (- - -) 50% Light (+ - -)
Light Medium/ Fawn 20% Very Light(- - -) 60% Light Medium (+- -) 20% Medium (++-)
Medium/ Tan 5%V.Light (---) 30% Light (+- -) 60% Medium (++-) 5% Dark(+++)
Medium dark/ Copper 20% Light (+--) 60% Medium (++-) 20% Dark (+++)
Dark/ Russet 50% Medium (++-) 50% Dark (+ + +)
Very Dark/ Mahogany 100% Dark (+ + +)
So when breeding, it is important to realize that many variations can result in a single litter, and that these results, statistically, can be predicted.
EXAMPLE #1:
Cross a rabbit with a Light/Medium(Fawn) rufus factor (++- - - -) to a rabbit with a Medium dark (Copper) rufus factor (++++ - -) and the offspring from that single breeding could have rufus appearance ranging from Light (+ - - - - -) to Dark (+++++ -).
The odds of getting these rufus colors, from chart#4 are :
The Light Medium (rufus) Doe (++ - - - -) can offer to the breeding only :
20% V.Light (- - -), 60% Light Medium (+ - -), and 20% medium (+ + -)
The Dark Medium (rufus) Buck (++++ - -) can offer to the breeding only :
20% Light (+- -), 60% Medium (++ -), and 20% dark (+++)
Multiplying these together produces the following possible outcomes:
Light + - - - - - .20 (+--) x .20 (+--) = .04 4%
Light Medium ++ - - - - .60(+--)x .20(+- -)=.12 & .60 (---)x .20 (++-)=.12 24%
Medium +++ - - - .20(---)x.20(+++)=.04&.60(+--)x.60(+--)=.36 &
.20(++-)x.20(+--) =.04 44%
Medium Dark ++++ - - .60(++-)x .20(++ -)-=12 & .60 (+--)x .20 (+++) =.12 24%
Dark +++++ - .20 (++-) x .20 (+++) = .04 4%
100%
The total, when calculated correctly, will always equal 100%.
A similar example to either extreme (darker or lighter parents) shows that the darker or lighter the pairing (that is, both) of the parents are, the more the offspring will be more like those parents, and the outcomes will be less a broad spectrum of rufus coloration.
EXAMPLE #2
Cross a rabbit with a Medium (Dark/Copper) rufus factor (+++ - - -) to a rabbit with a Dark (Russet) rufus factor (++++ + -) and the offspring from that single breeding could have rufus appearance ranging from medium (+++ - - -) to Very Dark (++++++).
The odds of getting these rufus colors, from chart#4 are :
The Medium (Dark/Copper) Doe (+++ - - -) can offer to the breeding only :
20% Light (+ - -), 60% Medium (+ + -), and 20% Dark (+ + +)
The Dark (Russet) Buck (+++++ -) can offer to the breeding only :
50% Medium (++ -), and 50% Dark (+++)
Multiplying these together produces the following possible outcomes:
Medium +++ - - - .20( +--) x .50 (++- )= .10 10%
Medium Dark ++++ - - .60( ++-)x.50(++- )=.30 & .20(+-- )x.50(+++ )=.10 40%
Dark +++++ - . .60(++- )x.50(+++)=.30 & .20(+++ )x.50(++- )=.10 40%
Very Dark ++++++ .20(+++ ) x .50 (+++ )= .10 10%
Thus, only 10% are lighter than the lightest parent, and 10% are darker than the darkest parent.
Finally, it is easy to see that once the deepest color is attained in your Castor or Red Mini Rex, (that would be Very Dark (++++++), then each subsequent breeding from such animals can only contribute (+++) and so all young can only be Very Dark rufus. 100% of the young are consistently dark.
This is why there is such small variation in the known ‘high rufus factor’ breeds, such as the consistently dark New Zealand Red or the Thrianta red.
This also means that, once the darkest rufus can be attained in Tan Mini Rex, they also will be able to breed without regard for that element in their color development. (That is a long way off, as are the darkest reds.)
The above is what is regarded as a ‘well reasoned speculation’. It is believed to be an applicable theory, but not yet fact. No one has taken the ‘rufus’ modifier to the extent that it needs to be taken in Mini Rex. Perhaps this will encourage some breeders to move forward with their ‘rufus’ experiments and prove or disprove elements of this proposal.
3/05/2006