A question from another forum has lead me to thinking about this one....

I understand that a fox-red labrador is merely a very dark shade of yellow. However, given that the majority of yellow (& yellow carriers) do not produce this shade, yet some dogs regularly produce the colour. This leads me to think that there must be another genetic component which causes some dogs to throw the darker shades.

Can any genetics expert shed any light on this for me? Just an academic question, I'm not looking into breeding any 'designer colours'! 

What a pity that John is no longer posting - he would have had valuable information here :(

i saw one at crufts on sat, doing gamekeeper trials, was not sure it was a lab havnt seen one before,

you lean something new every day

jackie

There is, apparently, the influence of another locus in the true fox-red colour, besides the 'normal' yellow 'ee'

Julie Vaughan is the person on here who is most qualified to answer, but I can quote from the Labbies.com site:   (you DID ask.......)

Jo and the Casblaidd Flatcoats

Fox-reds

Breeders of "true fox reds" will quickly point out that some yellow Labs professed to be "fox-red" are really more dark tan than red and are therefore, not "true fox-reds". The difference in concentration of red color (determined by the "ay" or "as" allele of the A locus) is dependent upon the alleles at the C locus. The "C" allele allows for full expression and intensity of red tones, while the "cch" allele will dilute the red to a clear tan color.

Therefore, the genotype of each color variation is:

ay_B_ C_ee = True Fox-Red
as_B_C_ee * = True Fox-Red with Saddling**

ay_B_ cch _ee = Pseudo Fox-Red
as_B_cch_ee = Pseudo Fox-Red with Saddling**

* the underline denotes that the gene locus may be homozygous or heterozygous with a less dominant allele present at the partner-chromosome gene locus
** Labs with this genotype demonstrate the red coloring localized to certain areas of the body.

The "as" allele produces the "saddling effects" seen in many yellows in which there appears darker yellow pigmentation on the back,
ears, legs, etc. compared to areas of light yellow on the shoulders, neck, and underside. The "as" allele also increases intensity of phaeomelanin, but restricts its production to the former mentioned areas on the Lab. 

The observation that there appears to be no solid fox-red or solid "pseudo" fox-red Labs may be explained by Little's hypothesis that the combination of an "ay" in a homozygous "e" (yellow) dog is lethal.  If Little's hypothesis is correct, then this would mean that all fox-red or "pseudo" fox-red Labs must be:   as_B_C_ee   or    as_B_cch_ee, respectively.



Medium to light shades of Yellow

    Medium yellow is probably the most common yellow coloration observed in Labs. The ranges in the shades of the yellow coloration, however, can be quite extensive. Medium yellows, listed from darkest to lightest, are produced by the following genotype combinations:

AsasB_ C_ee

AsasB_ cch_ee

AsAsB_ C_ee

AsAsB_ cch_ee



     Those yellows  heterozygous "As" "as" will produce less phaeomelanin because the As allele encodes a phaeomelanin suppressor. However, the alleles of the A locus are incompletely dominant, so some phaeomelanin will be produced because of the as allele.  The phaeomelanin intensity will be further controlled by the "C" locus, hence the intensity of the yellow may be stronger in these heterozygotes carrying the "C" allele and lighter in those carrying the "cch".  The homozygous "As" Labs do not produce red pigment at all because the suppressor will completely block phaeomelanin production by the mutant Mc1r   encoded by the homozygous "e" allele.  As a result, the coat will appear a cream color and will appear almost white if the "cch" allele is the most dominant allele at the C locus. Additionally, Labs homozygous "As" will show an even distribution of yellow color devoid of shading.

Hi Jo

You beat me to it :-)

That site does make Lab colour seem more complicated than it actually is, by bringing in the A locus patterns.  A locus very rarely expresses in Labs as the vast majority are KK so preventing expression of A.  Recessive kk would be needed for this, so unless we are talking about rare tanpoint or sable Labs, I tend to ignore A for simplicity :-)

Also the bit about Ay and ee combination being lethal, as hypothesized by Little, is now disproved.

Julie

Hi,
  It was my fox red labrador dog that you saw at crufts on the gamekeeper day. He is FT Ch Tasco Rouble of Bedgebrook. Hope that you liked him.
    Best wishes
       Gilly

Gilly,

I understand that he had an amazing trialling season this winter. Many congratulations!

   I HAVE JUST Been watching you and your Dog on Ret champ Dvd you did very well

  Has John retired ? i have missed him lately

  Yorker

If it is JohnW he is busy on another website

Hi Megaloo, welcome to this site :D and yes it is JohnW, he is John on this site :)

Thanks K I thought it was, because of the knowledge he shares, there could not be 2 Johns with that amount of knowledge?/

John W is now on www.labradorforums.co.uk- he is a mine of information! Though his reporting of KC rules re radiographing hips for scoring makes me think the KC is out of touch wit the real world!

Yellow is the generic term in genetics for phaeomelanin (light) pigment and this can range from light cream/white (Westie) to dark red (Irish Setter).  The genotype which produces this is the recessive ee.  I know this is going to sound stupid but ee yellow is not a colour but a pattern,  the  pattern being all-over-phaeomelanin.  It's the shade of phaeomelanin which determines the colour and this is controlled by other genes and/or modifyers.  All yellow Labs are ee so yes, there have to be other genes in the breed gene pool which alter the shade of phaeomelanin.

One series that influences shade is the C locus with dark shades dominant over light.  There has been another locus suggested, the Int series which is said to work the opposite way ie lighter shades dominant over dark. 

As Lab yellow shade varies from very light to very dark they no doubt have full complement of these modifyer genes in the breed.

Julie

Thanks ladies, I was right about the other genetic component, but am not convinced I understand exactly why!!! :-)

My own yellow was one of four in the litter all of which were very distinctly different shades of yellow, ranging from off-white to fox-red.

Many thanks for taking the trouble.

Which shade of yellow is yours, then , Havoc?

Jo

Quite pale, she was the second lightest (or third darkest, if that makes sense!) of the four. Darkest was retained by the breeder, the mid-yellow was already booked so I had a choice of two. Nothing to choose between them temperamentwise so I just picked the one with the more attractive face. I've never been too fussy about colour.

She turned out a very smart worker, Won out of novice trials quite easily, got a CofM in a two day Open, but I havent had the time to do her justice in Open trials. Not bred from, an uneven hip-score put me off and a pyometra took the decision away.

my cousins lab was a very dark colour with a red tint he was a beautiful dog sadly he was killed a few weeks ago :-(
he was picked up as a stray at about a year old

georgina