My thoughts on Mottling
For Beginners
Mottling is a recessive gene indicated by the symbol mo,
so if a bird has mottling it is written mo/mo
if it is split for mottling it is written Mo+/mo
If it doesnt carry the gene it is written Mo+/Mo+
A mottled Pekin refers to a black bird, who should be silver based who has two copies of the mottling gene.
Mottling seems like a fairly simple gene that does some fairly simple things. I dont think we know the full story though.
Mottling is responsible for the lack of pigment on the tip of the feather. It does not cause a white tip, but rather a lack of pigment at the tip.
Often we see a black band inbetween the white tip and the rest of the feather, which is ground coloured.
Mottling is said to only express when it is pure(homozygous), i dont believe this to be the case, rather i think it is incompletely dominant.
Mottling does seem to express on some heterozygous birds, on some backgrounds.
This leads me to think perhaps there are other genes also at play here, i doubt there is one simple mottling gene responsible on it's own for such a massive variation of effects.
Look at the difference between the Speckled Sussex and Ancona for example. The lack of expression in the neck and saddle of Pekins?
My personal view is that there are undocumented modifiers at work here, leading to the difference in expression across many breeds.
Mottling is responsible for the lack of pigment on the tip of the feather. It does not cause a white tip, but rather a lack of pigment at the tip.
Often we see a black band inbetween the white tip and the rest of the feather, which is ground coloured.
Mottling is said to only express when it is pure(homozygous), i dont believe this to be the case, rather i think it is incompletely dominant.
Mottling does seem to express on some heterozygous birds, on some backgrounds.
This leads me to think perhaps there are other genes also at play here, i doubt there is one simple mottling gene responsible on it's own for such a massive variation of effects.
Look at the difference between the Speckled Sussex and Ancona for example. The lack of expression in the neck and saddle of Pekins?
My personal view is that there are undocumented modifiers at work here, leading to the difference in expression across many breeds.
Here on a mottled partridge, the hackle feathers all display a strong black band in between the white tip and the ground colour.
On the cushion the band is often missing. this seems to miss the black band on feathers that already have some form of pigment modification, in this case, patterning gene.
Perhaps with modifier genes like Pg and Db, mottling does not express as well. These are just observations though. Maybe because the black is already being effected by other modifiers, it doesnt allow for the extra black band.
Mottling doesnt only appear as white, leakage can sometimes be seen in the white tip of the feather. Here on a split male (S/s+), the yellow is leaking into the mottles.
Here is the same split male a few months older, notice the brassiness coming into the white tips.