A tricky player in the genetics of coloured…
By Wendy Allison, Wairarapa
In the last article we looked at how the alleles your sheep has on the Agouti locus affect how much white it will have on it, whether it’s all white, white markings on colour, or all coloured. But, if you remember in the first article we mentioned there are three main loci (places on the DNA) that affect colour.
The second locus we’re interested in is called Brown, and it determines what colour your sheep’s skin will be. There are only 2 options – black or brown – hence the name. Most sheep have black skin because black is dominant. Even white sheep, if you look at the bare part of their nose, their hooves, and around their eyes, usually have black skin.
However, some sheep have brown skin, hair, and wool. This is often called moorit.
Brown in sheep is caused by a mutation that causes breakdown of a protective chemical called eumelanin in the sheep’s skin cells, causing the skin and any hair or wool that grows out of it to be brown.
Brown skin is recessive to black skin. If you remember in the first article with the punnett squares, we showed how different dominant/recessive alleles might affect the colour of a lamb. It’s the same for black skin and brown skin. So, a lamb needs both the alleles on the Brown locus to be brown before the lamb will be brown. Any animal that only has one brown allele will have black skin – but could pass on the brown allele to their lambs.
Neither of the parents of the pictured brown lamb are brown themselves – Luci is self-patterned and Nero is light blue, and they both have black noses, feet, and eyeliner. While their wool has faded to brownish, it’s black on their legs and at the skin whereas the newborn lamb is obviously brown.
In this pic you can clearly see that the skin on her nose is brown, not black
in the close-up of Muppet as a lamb you can also see she has a white nose ring and a little moustache. This shows she has inherited the blue pattern on Agouti from her sire. If you remember, this is dominant to Luci’s self pattern. So we know that Muppet is a brown sheep with a blue pattern. Her wool will fade as she ages, but she’ll always be brown because it’s in her genes. NB: a sheep with two brown alleles on Brown that also has dominant white on Agouti will have brown skin but the wool will be white.
Muppet would have to be bred to another brown sheep or one carrying the recessive brown allele to get brown lambs. But, her lambs are both carrying one brown allele so they could produce brown lambs with the right mating. Another reason for keeping good records!