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Genetics of Coat Color

Referenced from an article published by The New Zealand Kunekune Assoc​​iation August 2007

How to understand the genetics of coat color.

First let's start with a basic summary about genes.   A gene is a genetic code of DNA-- you get one set of genes from one parent and one set from the other parent.  How the offspring turns out depends on which particular gene is from each parent and how the genes can interact with each other.  A simple example is a black piglet -- black is a dominant gene, so to get a black piglet one of the parents must have had a black gene.  A pig always has a set of 2 genes -- one is see (=dominant) but the other is usually hidden.  Sometimes the second gene is the same (e.g. double dominant) or it is a recessive gene.  This can get more complex, as sometimes another separate gene can modify the original color one, such as instead of black color you might get a brown piglet (due to the Chinchilla gene).When a pig is used for breeding, it might pas on either one gene (e.g. the dominant gene), or another (e.g. the hidden gene.) This means that the offspring can show up with a gene that you weren't expecting, as it was 'hidden' in the parent. One of the things that happens over time is that if you select for a certain type of color, you often increase the frequesncy of that color in your population.  This happens particularly with the recessive genes--if you select for ginger pigs (which is recessive) you might lose some of the dominant genes from your population. Coat color is a trait that is composed of several genetically controlledtraits.

Coat Color Genes in Kunekune

There appear to be 5 main color gene locations in Kunekunes.  These are the Extension (E), Agouti (A), Chinchilla (Ch), Dilute, and White Spotting genes. For each gene location, there can be more than one type i.e. they don't just come in a choice of 2 genes at each gene location -- for the Extension gene there is a choice of 4.  Then some of the gene locations influence each other, so what the final color is could be a combination of up to 5 differnet genes working together. The basic body color gene that has the main influece is the Extension genes:  Ed, E, ej, and e. Ed is dominant blackE is normal black. ej is dark ginger with black spots or patches.e is dark ginger. When the E type occurs, it allows the Agouti gene to be expressed (when it is not the E type, you don't see the agouti colors as that gene is blocked). In Kunekunes the Agouti gene seems to give 3 types:  As, ay, or aw. Pigs that have the E type (plus the Agouti type) are eirther black E(As), brown E(ay) or the true agouti color E(aw) of brown with a lighter underside and yellow tips on the end of the hair.  Piglets with the Agouti gene have longitudinal strips in their coat when young a sort of camouflage-like effect seen in young wild animals. The third main gene is the Chinchilla gene -- this is also seen in some other breeds of pigs such as the berkshire.  Where the chinchilla gene is the dominant form Ch, it modifies the main coat color.  This results in black coat being modified to cream with black spots, and the ginger color being modified to a cream color. Another modifying color also appears to act like a Dilute gene and changes the intensity of the color, so that the color is lighter than expected.  This could explain why, for example, some ginger pigs are dard ginger while others are a very pale ginger. The White Spotting gene is a recessive one, and allows spots or patches of white over the body, with a modifying gene altering the size and distribution or the white areas. To summarise, black is the most dominant color in Kunekunes.  Then the next dominant color is the black/brown range of clors affected by the Agouti gene.  The next level is the ginger with black spots color, (which is sometimes modified to cream with brown spots by the Chinchilla gene), then the most recessive color is the plain ginger color (sometimes modified to the cream color by the Chincilla gene). The cream color of some Kunekunes is different to the white color of the white breeds of pigs -- the cream color often has some ginger tones on parts of the body, and the skin is usually a grayish color that is not susceptible to sunburn.  If a Kunekune of any color is crossed with a white pig, all of the offspring will be white (although possibly with some black patches) as white is the most dominant coat color in pigs.  Selecting the Colors You Want to BreedEach pig carries a set of genes for color, with the dominant genes determining what color the pig is and the less dominant or recessive genes hidden.  If you want to know what possible color recessives a pig is carrying, you can find out what color its parents and litter mates were and try and work out what recessives it may carry on a probability basis.  When a pig is used for breeding, the color of the offspring may also help indicate what recessive both parents carry, although statistically not all color combinations will occur at any one time. For example, if you have a definitely black pig, its color genes could be one of seven main possibilities.  As Ed black is dominant, the second gene could be any of the four main Extension genes:  resulting in the possibilities being Ed.Ed, Ed.E, Ed.ej, or Ed.e.  Black can also occur with the second Extension gene E if combined with the Agouti gene (As), and as this is dominant over ej and e the other combinations possible for a black pig are E(As).E, E(As).ej, and E(As).e.  So if you mate 2 black pigs together, there are heaps of combinations of piglet color that can occur, especially if both parents are carrying recessive genes i.e. 2 pure black pigs could produce just about the whole range of colors (even ones with white spots). A ginger pig would have to be double recessive e.e as this is the most recessie and only occurs when the other more dominant genes are absent. A ceam Kunekune is really e.e (ginger) but with the Chinchilla gene Ch modifying it to cream, so you could use a cream pig to try to breed ginger pigs provided it didn't have a double dominant Ch.Ch combination. A ginger pig with black spots could be either ej.ej or ej.e.  If you wanted to breed plain gigner pigs and started wtih 2 pigs that were ginger with black spots, if the parents were both ej.ej you would never be able to breed ginger pigs without the black spots. The range of brown colors is extensive and difficult to categorise -- some are Agouti brown, some due to the Chinchilla gene (modifying black to brown), and some are such a pale brown as to be difficult to separate from the ginger color. Once a litter was produced from a brown boar and a ginger sow with black spots--the piglets were all different colors: black, brown, ginger with black spots, ginger, and cream.  Black is dominant (either Ed or E(As)), so the only way a black piglet could be born is for the boar to be genetically black but with teh Chinchilla gene present, so turning out brown rather than black.  Knowing that the boar had the longitudinal stripes when he was young meant that he carried the Agouti gene, so he must have been E(As) plus Ch.  The cream piglet produced was genetically e.e (ginger) but with the color modified to cream by the Chinchilla gene.  As there were ginger and cream piglets produced, both parents must carry the recessive e gene. So the boar was E(As).Ch.e and the sow was ej.e.  The piglets were E(As).e or E(As).ej (black carrying the Agouti gene, no Chinchilla gene, E(As).Ch.e. or E(As).Ch.ej (carrying the Agouti gene, but brown due to the Chinchilla Gene from the boar), ej.e (ginger with black spots), e.e (ginger), Ch.e.e (cream, Chinchilla gene from the boar).