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Genetics – Why a Brown Spotted Lamb is Like the Holy Grail

By Wendy Allison, Wairarapa.

In the last article, we looked at the Brown locus – the second of the three main determiners of colour in sheep, and the one that decides whether your sheep’s skin will be black or brown. Today we’ll be looking the third locus, which determines whether or not your sheep has spots.

Muppet is a good example of a sheep that is basically brown, but with a pattern on Agouti that gives her white markings on her face. She is not spotted.

Most sheep are plain coloured – whether that be white, brown, or black, the majority of their colour will be one of those. Any variation comes from their pattern as dictated by the alleles on the Agouti locus that we discussed in the second article.

Some sheep do have spots though. Spots come from the alleles on the third locus, which is imaginatively named the Spotting locus. Alleles on the Spotting locus can create white patches on the sheep’s skin and wool which override the sheep’s basic colour and make it spotted. The spots can be large or small, but they are always white.

In this case, plain colouring is dominant and spotting is recessive so this means a sheep has to have a copy of the spotting gene from each of its parents on the Spotting locus before it will have spots. If you go back to the punnett squares in my first article and substitute dominant plain colour (S+) and recessive spots (Ss) for white (W) and coloured (c), you can work out what combinations will produce spotted lambs.

This is just the first two possible combinations, try the others yourself!

Loki produced one spotted lamb and one dark blue lamb, because both she and the ram carry the recessive spotting allele

In the picture alongside, the ewe is plain self-patterned and the ram is plain blue patterned. Neither parent is spotted themselves, but they are both carrying the recessive allele for spotting, and here is the result. The spotted lamb has large white patches rather than the little flashes of white you’d see if it were a pattern. The skin under those patches is pink, because there is no colouration in those cells at all. While his nose and eyes are still black because he’s black on the Brown locus, if he had a spot on his face that covered the nostrils, his nose would be pink.

 

Cookie is from the same cross, but she has a white spot that includes her nostrils so her nose skin is pink

In this picture of Cookie you can see that her nose is pink but her eyes have black skin around them. This is because her Brown locus alleles are black, giving her a black skin colour as discussed in the article about Brown – but her pair of Spotting (Ss) alleles on the Spotting locus give her pink skin wherever her spots are.

Cookie was bred to a plain, self-patterned ram and her lamb was born plain, because he only has one spotting allele on his Spotting locus. But he would be able to produce spotted lambs if crossed with another sheep that has spotting in its genes.

 

 

 

Now that we understand the three loci and how recessive alleles must have a copy from both parents present to produce the recessive colours, you can see why brown spotted lambs are quite rare. To be brown and have spots, a lamb must have a set of recessive alleles on all three of the loci.

Photo credit: F Vasconcellos

That’s quite a lot of recessive alleles for one little sheep to have! We have not managed to produce one at our place yet, but there’s a chance we might get one from crossing the sheep below.

Spider was sired by a ram that carries the spotting gene so he may be carrying it too. Cookie was sired by a ram that carries the brown gene so she may be carrying it too. Between them, they could potentially produce a brown spotted lamb

Spider

Cookie

In the final article of this series, Genetics – Breaking the Rules, we will look at some exceptions

This Post Has 6 Comments

  1. Hi, I read your most helpful article. I have just bred a Wilshire ram lamb with a large brown spot on the middle of his back. So cute.

  2. I’m trying to find info on the colored horned Dorset. I have about a 100 hd of them. Been linebreeding for 15 plus years. It seems there isn’t much info out there that I could find. I would be interested if you have a lead. There aren’t many around. Thanks Terri

  3. I’m new to shepherding (~1 year). We culled our small herd and kept mostly the hair breeds. I’m creating my record books and don’t know how to classify some of these sheep. (They came with the small farm we bought, and the previous owner didn’t keep records.) I have one Barbados 4-horned ram and is twin, 2-horn. I have another blackbelly mouflon 4-horned ram. I think I’ve classified them fairly well, and I’m keeping the 4-horns for breeding.
    The ones I don’t know how to classify are my piebalds and spotted sheep. I have one ewe beauty that is a shorthaired blonde and white piebald with the frame and short hair of a Barbados. She lambed twins – a grey and white piebald and a chocolate colored ewe; both have Barbados frames and are shorthaired. Some of my other lambs this season are white with reddish brown markings and spots – they are hair sheep too – but not what I would call piebald. How do I classify these multi-colored patterned sheep?

    1. Hi,

      First I have to say that I’m not familiar with barbados sheep as we don’t have them here in Aotearoa. However, if the general genetic rules for sheep colour apply to these, any animal with irregular white spots in the coat is considered spotted. There are various spotting patterns (for example HST where the white is primarily on the head, socks, and tail) that are basically modifications of the “white on dark” basic spotting presentation. So it sounds like most of your animals ares potted, either with the markings you describe as piebald, or another spotting pattern.

      The other gene that may be involved is brown – from the sounds of things your animals are mostly brown, but you’ve produced a lamb that may have the more dominant black on the brown locus, the grey and white one. This would generally require either the sire or dam to also have black on the brown locus, and that would show as black nose leather and eyelid rims (if they aren’t affected by spotting and thus white).

      Alternatively, there may be modifiers in the brown or on the agouti locus that affect the presentation of the basic genes in blackbelly sheep that I don’t know about. 🙂 Sounds like you’re keeping detailed records though, so in a few years with more breedings you may be able to isolate what caused the grey.

  4. Hello . I’m from The carribean I have a black and dark brown speckled lamb . Mom is a black head dorper and dad is a Cuban red . He now started growing his horns . How rare is he??

    1. Hi Sandesh,

      Admittedly I know little about Cuban Red sheep but a bit of research tells me that they are capable of producing both spots and combinations of brown and black colouring. They aren’t supposed to grow horns. However, blackheaded dorpers are extension dominant which would normally produce lambs with their own black colouring. They are also usually polled but occasionally horned.

      My best guess for what’s happening with your lamb is that the dorper, rather than being EdEd (full dominant on the extension locus) is instead EdE+, and has passed the E+ to the lamb, allowing the other colours to express. Potentially he is not purebred, although this could also happen with purebred animals.

      In terms of how common this is, in Cuban Reds being this combination of colours appears to be fairly common, but the horns are not.

      Hopefully this answers your question!

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