Coat Colour Genetics – By Dr K Nicoll

Coat Colour Genetics – By Dr K Nicoll

Pig cells have strands of DNA that are organised into 38 pairs of chromosomes. The sequence of the DNA strands in these chromosomes results in what we call genes (coding sequences) – pigs have approximately 22,000 genes.

Each gene has a particular action or function, although many genes interact with each other so that the outcome of these thousands of genes is a well organised set of physical characteristics that we can see.

For coat colour there seem to be 5 main genes in Kunekunes that interact to produce a variety of coat colours and patterns. But some of the difficulty in understanding the genetics is due to the fact that an animal may have two sets of each gene, and because these genes interact with each other and some dominate so that their opposite gene is hidden (recessive), unless you can test a pig genomically it is often guesswork to try and work out which genes a pig actually carries in its chromosomes.

When a piglet first starts off as a fertilised embryo it has inherited one set of genes from the boar and one set of genes from the sow. Some genes are dominant, some are recessive, and some will be somewhere in between that. In most cases the colour in Kunekunes is a simple dominant-recessive relationship, but it is complex as multiple types of genes influence the outcome of the primary colour genes that we can see visually.

In Kunekues there seems to be 5 main types of colour genes:

• Extension
• Agouti
• Chinchilla
• Dilute
• White Spotting

The Extension gene is like the primary gene colour, which the other genes can sometime influence, and has 4 gene types:

• Ed = dominant black
• E (sometimes also called E+) = normal extension of black
• ej = dark ginger with black spots or patches
• e = dark ginger

As a piglet has two genes for the same characteristic, it depends on which is the dominant one and which is the recessive one as to what colour it turns out to be.

The Ed is the most dominant gene, and the e is the most recessive one.

In the table below the Extension gene combinations are shown with the most dominant gene listed first, along with the expected colour that is likely to result. Note that this is before the other genes also have their effects added in, so it gets way too complicated to try and add all those in as well!

When the E gene (sometimes called the ‘wild’ gene or E+) is present it allows the Agouti gene to be expressed, but if any of the other types of Extension genes are present the Agouti gene is usually completely hidden or ‘inactive’. Pigs with the E gene tend to have the agouti colour pattern superimposed over their primary colour. In piglets this is seen as a camouflage-like longitudinal striping pattern that disappears as they get older, and this pattern is seen in wild types of pigs such as European wild pig and the Captain Cooker pig.

The Agouti gene can result in the following colours:

• E(As) is black
• E(ay) is brown
• E(aw) is brown with a lighter underside colour to the body, and with yellow tips on the ends of the hair

In kunekunes there seems to be a ‘dominant’ Chinchilla gene similar to some other breeds of pigs (Asian breeds, Berkshire etc). This gene interacts with the primary colour gene and modifies it so that black (Ed) becomes brown, ginger with black spots (ej) becomes cream with brown spots, and a ginger pig (e) becomes a cream colour. The cream colour in kunekunes is different to the white colour seen in other breeds of pigs, as the cream often has ginger tones to it and the skin underneath often has a blue-grey pigmentation.

The Dilute gene is also a modifying gene, and changes the intensity of the colour so that it is lighter than expected. This explains why some ginger pigs are a dark red or chestnut colour while others may be a pale ginger colour. This one can be hard to determine if it is present, as many pigs change to a lighter colour anyway as they get older.

The White Spotting gene is a recessive one, and allows spots or patches of white over the body. There also seems to be another gene that modifies the effect of the White Spotting gene by altering the size and distribution of the white areas.

There are also a few other colour genes that can be seen in some kunekunes – an example is a white saddle or belt, which is caused by a dominant gene. Although the gene probably originated from a saddleback or hampshire pig that was crossed with a kunekune, there have historically been some kunekunes that are belted going back for many generations. Although they raise the issue of the purity of the bloodline, they are an interesting colour combination that some people like. While most of the belted kunekunes are black with a large white belt, some are ginger with a white belt, and some also have additional spots of colour as well.

Selecting colours you want to breed

As kunekunes come in a range of colours, if you prefer to breed piglets of a particular colour or degree of spotting then it is a good idea to think about the potential genetics behind the colour so that you can aim to breed the combination of parents that is likely to give you the ideal outcome. Fortunately kunekunes tend to have several piglets in a litter, which increases your chances of getting at least one of the ‘right’ colour you want.

An example is if you want to breed pure ginger piglets – of all the colour combinations for the Extension gene, out of the 16 potential options there is only one combination (e.e) that will result in a pure ginger piglet. But then if you have a sow that is either ginger (e.e) or ginger with black spots (ej,ej or ej.e), unless the boar you mate her with is carrying the e gene (Ed.e or E.e) you will not get any ginger piglets. If he happens to be Ed.Ed , Ed.E or E.E the recessive e gene will not have an opportunity to be expressed, and the piglets will tend to be black.

Remember that a cream coloured kunekune is ginger modified to cream, though, and your ‘plan’ for a ginger piglet might result in a cream piglet instead. On average pigs with the Chinchilla gene will pass that gene on to about half their offspring, so if you are aiming for ginger colours it pays to avoid using cream pigs.

When the kunekune was rediscovered as a breed there was a predominance of particular colours, particularly black, but as time has gone by the numbers of multi-coloured pigs has gradually increased so that there is now a wide range of colours and patterns available.
By selecting the colour of your breeding stock you can affect the outcome of the colours of the piglets that might occur, which can mean they are easier to sell if they are popular colours.

Examples of different colour patterns