Friday, July 8, 2016

New Zealand Rabbit Genetics: Coat Color: It's In The Genes




To reiterate what we talked about in my first article on dominant and recessive genes, a rabbits chromosomes are strings of DNA that act as building blocks or blueprints that determines the final characteristics or traits of the animal. Each chromosome has an individual spot or location (loci) in which a specific gene is attached. The buck and doe each contribute one part of their chromosome's to their offspring. When these two chromosomes combine together they form a chromosomal pairing in which each chromosome supplies one allele to make a genetic pair. These allele pairings then act together, alone or in combination with other alleles and gene modifiers to determine a rabbits overall coat and hair appearance.

In this second article of the series, we will be examining how a New Zealand (NZ) rabbits hair color is determined by a combination of multiple genes and their allele pairings. The combination of allele pairings of each gene act in conjunction with other genes to produce a variety of different colors and patterns. A rabbit has only two possible pigments that can be expressed in its hair, dark brown and yellow. The absence of both pigments results in albinism (white fur). All of the possible hair colors in a rabbit's hair shaft are simply combinations of these pigments or lack thereof. This genetic expression can appear on the same or different hairs, in certain patterns, and in different intensities. Because we are going to be looking specifically at the genetic makeup of the New Zealand breed, there will be some genetic color traits found in other breeds that are not present in New Zealand's.

In NZ rabbits, as with most breeds, there are 10 genes (A, B, D, C, E, En Du, Si, V and W) each with multiple alleles (gene variants) that determine the primary color and depth of a rabbit's coat. There are other factors and color modifiers (rufus modifiers, plus/minus) that work in combination with these genes and their allele's to control the intensity and or depth of certain colors and or patterns. These color modifiers are not single genes, but multiple ones that work in combination to create a specific color pattern.

A-Series Genes: Agouti (A_) allele, and Self (a_) allele
Possible Allele Pairings: Agouti Rabbits (AA, Aa), Self Colored Rabbits (aa)

The A-Series of genes has only two possible possibilities in NZ rabbits, agouti (A_) or self (aa). While other breeds carry the Tan (at) allele, purebred NZ rabbits do not.

The agouti (A_) allele has complete dominance over the self (a_) allele. It produces a rabbit with a white or cream (depending on modifiers) hair color on the belly, eye circles and inner ear, and the rest of the hairs will be banded. So when you separate the hairs and closer examine them you will usually see three distinct color rings. The outermost color ring is determined by the B-series and D-series genes and their allele's (see below), the middle ring will generally be white to bright yellow, and the bottom ring will be white to slate gray. This genome is responsible for the “natural” or “normal” color of wild rabbits. In New Zealand rabbits this color pattern is often called chestnut.

When two recessive self (aa) alleles are paired together it produces a NZ rabbit that has a coat completely made of one color. Therefore, a rabbit with a self (aa) allele pairing is bred with another rabbit with the self (aa) allele pairing, they should never produce any agouti offspring. If you are looking to breed for consistency of color in your heard, then it is important that you acquire both male and female rabbits with a self (aa) gene. The self color is sometimes called 'solid' by some breeders.



B-Series Of Genes: Black (B_) allele or Brown (b_) allele
Possible Allele Pairings: Black Colored Rabbits (BB, Bb), Brown Colored Rabbits (bb)

Almost all rabbits regardless of breed will carry are either the black (B_) or brown (bb) allele. The B-series gene then determines whether the rabbits base coat color is black or brown. Because the black (B_) allele has complete dominance over the brown (b_) allele. Black is the most common color, as the allele pairings (BB) or (Bb) will always produce a black or blue rabbit (see NZ Blue later in this article), while the recessive (bb) allele pairing will always produce a brown rabbit. Therefore, if two rabbits both have the recessive brown (bb) allele pairing they will never produce any black offspring. If any pair of rabbits produce brown offspring, then both the buck and doe must have had at least one brown (b_) allele.

Some rabbits look like they have a brown coat, but they are not really brown. The most common example of this is the agouti (see above), sometimes called the “natural” or “normal” color of rabbits. While an agouti or cottontail rabbit may appear to be brown in color, their coat is actually made of different layers of banded phoemelanin (yellow) and eumelanin (dark brown) hairs. This combination of colors may give the appearance of brown rabbit, but a brown rabbit must have the (bb) allele pairing.


C-Series Of Genes: Complete (C_) allele, Incomplete (c_) allele
Possible Allele Pairings: Complete Colored Rabbits (CC, Cc), Albino Rabbits (cc)

The C-series of genes determines whether a rabbits coat has complete color or no color. The complete (C_) allele is dominate to the incomplete (c_) allele. The dominant complete (C_) allele allows all four of the dark and all three of the yellow pigments to be present in the hair shaft. This allows for full color development of the rabbits coat and works with the E-series of genes and their alleles to produce ticking or steel tipped colors in rabbits that carry the agouti (A_) allele. The New Zealand Black (NZB) is an example of a rabbit that carries the complete dominant allele. When a rabbit receives two incomplete or recessive (c_) alleles from it's parents it is classified as an albino. The recessive (cc) allele pairing not only blocks all the color of all the pigments along the hair shaft, it blocks all expression of color in the rabbit producing a white rabbit with red eyes (REW). The New Zealand White (NZW) rabbit because it has the recessive (cc) allele pairing has a coat as well as eye color that lacks any color pigment. They are in essence albinos, however they are carriers of all the other color allele's you just cannot physically see them. You may however see some of these allele's show up in their offspring when bred to a non-white rabbit.




D-Series Of Genes: Dense (D_) allele or Dilute (d_) allele
Possible Allele Pairings: Dense Coat (DD, Dd), Dilute Coat (dd)

The D-series of genes determines the depth of color of the coat of the rabbit. Dense (D_) has complete dominance over dilute (d_), rabbits with at least one dense (D_) allele have full color shades that are are darker (black or chestnut), and generally have brown eyes. Rabbits with a dilute (d_) allele have a lighter more sedated or dilute colored pigment in the hair shaft causing the coat to be lighter in color. Any combination of allele pairing in which there is at least one dense allele (DD, Dd) will produce a rabbit with a dense coat with (DD) being the darker of the two. Rabbits with the dilute (dd) pairing have the lightest or most dilute coat color. If you want to increase the depth of coat color in your rabbit's bloodline, then breeding a rabbit with a (DD) allele can help you accomplish this while breeding a rabbit with a dilute (dd) allele pairing will soften or mute the color.

When a rabbit with a dilute (dd) allele pairing also carries one of the black (BB, Bb) allele pairs, the coat color is changed or diluted from black to blue and causes the eye to be gray-blue. So we see that the B-series gene and the D-series gene when combined can produce a totally different color of rabbit. Breeders of NZ's have been developing a genetic line of New Zealand Blue's (NZBL) for a few years now, but this color has not been approved by the ARBA so there is no breed standard as of yet. Therefore any rabbit that is blue in color must have a complete dilute (dd) allele pairing.


E-Series Of Genes: Steel Extension (Es_) allele, Normal Extension (E_) allele,
Non-extension (e_) allele
Possible Allele Pairings: Steel Tipped Rabbits (EsEs, EsE, Ese), Black Rabbits (EE, Ee), Red Rabbits (ee)

The E-series of genes work in combination with the C-series of genes and the rufus modifier to make a variety of small and subtle changes to the pigments in the rabbits hair shaft that determines it's overall coat color. There is a lot going on with this gene series; not only are there six possible allele pairings (EsEs, EsE, Ese, EE, Ee, and ee), there is more than one dominant gene although there is a specific order of dominance that has to be taken into consideration.

In E-series genes, the steel extension (Es_) allele is dominate to the normal extension (E_) allele, which is dominant to the non-extension (ee) allele. The (Es_) allele works in combination with the agouti (A_) allele and is responsible for producing the ticking or steel patterns (Gold or Cinnamon tipped) in some NZ rabbits. This combination of (A_, Es_) alleles work together to accentuate or darken the characteristic agouti type landmarks (eye circles, triangle at nape of neck, feet, legs and the inside of the ears) of some rabbits. So in order for a NZ doe to produce kits with steel characteristics (tipped hair coloring) either the buck or the doe must carry an agouti (A_) allele. If both rabbits in the breeding pair carry the self colored (aa) allele pair, they cannot produce kits with steel tipped fur. In NZ rabbits steel-tipped kits are most often seen when a NZR (which carries the agouti gene) is bred with a self (aa) colored rabbit. Obviously a NZ chestnut agouti has the potential to produce steel tipped kits, but most breeders who sell breeding stock do not keep chestnuts as part of their breeding program.

The normal extension (E_) allele allows the complete expression of dark black/brown pigment in the hair shaft (New Zealand Black). You have to remember while the (E_) allele allows the complete expression of the black/brown color, it is not the dominant allele here, rather it is recessive to the steel (Es_) allele that is the most dominant allele of the series.

While the (E_) allele allows complete expression of the black/brown color, the non-extension (e_) allele when paired (ee) together removes or suppresses all or most of the black or brown pigment in the hair shaft leaving yellow or orange producing a New Zealand Red (NZR) rabbit.


En-Series Of Genes: English Spotting (En_) allele, Self Colored (en_) allele
Possible Allele Pairings: Charlie Pattern (EnEn), Broken Pattern (Enen), and No Pattern (enen)

In the En-series of genes (sometimes called “plus/minus” or “blanket/spot”), the English spotting (En_) allele is dominant to the self colored (en_) allele. The (Enen) allele pairing produces normal spotting of the rabbits coat, rabbits with this allele pairing are known as 'brokens'. The (EnEn) gene pairings produce less spotting of the rabbits coat than the (Enen) allele pairings, with the focus of the spotting generally around the head area. Rabbits with the (EnEn) allele pairing are known as 'charlies'. The final possible allele pairing is (enen) which as mentioned causes the hair to have normal coloring without spotting.

In addition, the allele pairings of En-series gene work in combination with the allele pairings of the C-series gene and other color markers to make a variety of small and subtle changes to the color patterns seen in NZ 'broken' and NZ 'charlie' rabbits. The amount and location of the spotting in 'broken' and 'charlies' can also be affected by other color modifiers.




The Other Genes (Du Si, V, and W)

Du-Series Of Genes: Absence of Dutch pattern (Du_) allele, White Belt Dutch Pattern (du_) allele
Possible Allele Parings: Solid Color Rabbits (DuDu), (Dudu), Dutch Pattern Rabbits (dudu)

The (Du_) color gene represents the Dutch color pattern. In a Dutch pattern the front of the face , front part of the body, and rear paws are white, the rest of the rabbit has colored fur. The Dutch pattern (Du_) allele is dominant to the white belt Dutch pattern (du_) allele. The (DuDu and Dudu) allele pairings are present in solid colored rabbits causing no dutch patterns. All pure breed NZ rabbits are (DuDu). Since we are specifically talking about genetic coloring and patterns in NZ rabbits, this is all we need to know about this gene.


Si-Series Of Genes: Non-Silvering (Si_) allele, Silver (si_) allele
Possible Allele Parings: No Silver Color (SiSi), Silver colored tips (sisi)

The Si-series of Genes is determines whether the rabbits coat has white and/or silver tipped hairs intermingled throughout the rabbits coat. The (Si_) allele is dominant to the (si_) allele. Rabbits with the (SiSi) allele pairings have normal colored coats (no white or silver tipped hairs), while the recessive (sisi) allele pairing produces white and silver tipped hairs intermingled throughout the rabbits coat. All pure breed NZ rabbits have the normal (SiSi) allele pairing and therefore have no white or silver tipped hairs caused by this Si-series gene. Since we are specifically talking about genetic coloring in NZ rabbits, this is all we need to know about this gene.


V-Series Of Genes: Normal Coat (V_) allele, No Color (v_) allele
Possible allele Pairings: Normal coat (VV), Vienna Carrier (Vv), Blue Eyed White (vv)

The V-series of gene (a.k.a Vienna White) produces a rabbit with a normal coat color. As with most allele's the (V_) allele is dominant to the (v_) allele. Almost all rabbits carry the (VV) gene pairing which produce a normal coat color. The recessive (vv) gene pairing produces a blue-eyed white (BEW) rabbit, while the (Vv) pairing indicates that the rabbit is a carrier for the Vienna White gene. All NZ rabbits carry the (VV) gene, there are no blue-eyed NZ rabbits so none of the breed can carry the (Vv) or (vv) gene pairing. Since we are specifically talking about genetic coloring in NZ rabbits, this is all we need to know about this gene.


W-Series Of Genes: Normal Width (W_) allele, Double Width (ww) allele
Possible allele Pairings: (WW), (Ww), and (ww)

The dominant normal width (W_) gene produces a yellow or white agouti color band in the hair shaft producing a normal coloring. The recessive double width (ww) gene doubles the width of the yellow or white agouti band in the hair shaft causing the rabbit to have the characteristic agouti pattern areas such as: eye circles, triangle at the nape of the neck, feet, and legs, as well as the inside of the ears and belly (typical of the new Zealand Red).



Modifier Genes

The Rufus Modifier (polygene):

It is unique in that it is a stand alone gene and does not rely on any other particular allele. As it's name implies, this gene modifier works in combination with other genes to intensify the red/orange color of the agouti coat in New Zealand Red (NZR) rabbit's. A NZR rabbit with multiple rufus modifiers will have a darker, richer color red coat. A NZR with fewer rufus modifiers will have lighter, duller red color. The rufus modifiers are denoted as a number of plus (+) signs at the end of the basic genome of red colored rabbits.

So here is where it gets a little sketchy. Most of the information I can find simply lists what the rufus polygene does, but does not give a definite idea of the number of rufus modifiers found in NZ rabbits, however my best educated guess is that there are five. So how did I come to this conclusion? The British Rabbit Council (BRC) actually lists the genome and breed standard for red rabbits on there website as: A_B_C_D_ee +++ rufus modifiers. From this information along with other information I have read, I believe that the NZR can have up to five rufus modifiers (+++++) with three (+++) being in the middle or the breed standard. If this is the case, then a NZR rabbit with five (+++++) rufus modifiers would have the most intense red color, and a NZR with two (++) or less would have a very light washed out color red.

Most Intense Red Color: (+++++)
Balanced Red Color: (+++)
Weak Red Color: (+) or (++)


Plus/Minus Modifier Genes

The plus/minus modifier genes work with the En, Du, and V genes to increase or decrease the amount of spots or patterns of a rabbits coat. The more plus modifiers that rabbit has, the more spots or colored hair pattern they will have, the more minus modifiers your rabbit has, the fewer amount of spots or colored hair pattern they will have.


Color Intensifier Modifiers

The color intensifier modifiers. These modifiers can either darken the spots of color and or the overall color of the rabbits coat, or lighten it to a more diluted shade. I will have to admit that I cannot find any additional information on what particular types of color intensifier modifiers there are New Zealand rabbits. Perhaps if I purchased a book that does a through in depth study of rabbit genetics it would mention what exactly these modifiers are, but at this point this is all the information that I could find on the subject.


New Zealand Rabbit Breed Basic Genome or Genotypes

Below are the listed basic genomes or genotypes for the NZ breed of rabbits with all 10 color genes represented. As all NZ rabbits carry the (DuDu), (SiSi) and (VV) allele pairings you could drop these from the listing (must people do) but for the purposes of this article, I wanted to try and give your the most information possible regarding the breed.

Agouti (Chestnut): A_, B_, C_, D_, E_, En_, DuDu, SiSi, VV, W_
Black: aa, B_, C_, D_, E_, En, DuDu, SiSi, VV, W_
Blue: aa, B_, C_, dd, E_, En_, DuDu, SiSi, VV, W_
Red: A_, B_, C_, D_, ee, En_, DuDu, SiSi, VV, ww +++
White: A_, B_, cc, D_, E_, En_, DuDu, SiSi, VV, W_

The Brokens:

Black: aa, B_, C_, D_, E_, Enen, DuDu, SiSi, VV, W_
Blue: aa, B_, C_, dd, E_, Enen, DuDu, SiSi, VV, W_
Red: A_, B_, C_, D_, ee, Enen, DuDu, SiSi, VV, ww +++

The Charlies:

Black: aa, B_, C_, D_, E_, EnEn, DuDu, SiSi, VV, W_
Blue: aa, B_, C_, dd, E_, EnEn, DuDu, SiSi, VV, W_
Red: A_, B_, C_, D_, ee, EnEn, DuDu, SiSi, VV, ww +++


Conclusion

So there are 10 color genes plus a variety of color modifiers that contribute to make up your rabbits coat color. The reality of the NZ rabbit makeup is that since (according to my research) all NZ rabbits carry the (DuDu), (VV), and (SiSi) allele pairings, most people do not examine these genes when they are determining the genome or genotype of the NZ rabbit. It was goal in this article however to give you the most in depth information possible so that you could examine your livestock and begin to understand the genetic makeup of the NZ rabbit. In the third and final article of the series 'Putting It All Together', I will show you how to put this information together to determine the possible genetic genome of your rabbits without having to do any DNA testing. It may not be as accurate as a DNA test, but it the tried and true technique that has been used by breeders for hundreds of years, way before DNA was even discovered.

Now I am not a geneticist, rather just a humble breeder of New Zealand rabbits that happens to have a medical background so do understand something about genetics. Having said that, I have tried to make sure the information provided in this article is as accurate as possible. If you see an error in my conclusions and have additional information regarding the subject, please feel free to leave me feedback so that we can discuss your findings. As always, if you have found this article interesting or informational please share it with your friends. Don't forget to follow us on Facebook or on Google+ for the latest articles on our blog related to raising your own meat rabbits.

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