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Discussion Starter · #1 ·
I've been puzzled over the colour bands in ticked mice. I understand that the basic agouti (wild) mouse has 2 colour bands - black base, yellow tip. Is this correct, or do they have black base, yellow middle and black tips?

My confusion comes from the standards for the diluted colours. Some varieties have two bands, (undiluted - black base, yellow tips) others have three (black, then yellow, then black tips). Can anyone shed any light on why this is? Perhaps the two banded mice actually have three, but the third is hidden or not formed?

My second question is in relation to the two sections of black in the ticked mice which have three bands. When they are diluted, it appears that the black base is affected differently to the tips - ie slate base to the hair, diluted (cream or white) middle section, with black tips. This occurs with c-dilutes. How is it possible for the dilute to affect two sections of black in the one hair differently?

I suspect it has something to do with the way the dilute interacts with the cells that comprise the hair, and these may be different at the base to the tips. Does anyone have any ideas?
 

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Now you've got me wondering where to find a reference for this question. I always thought agouti had three band on each black, red/yellow, and no I don't know what the third one is. Gonna look around and see what I can find.

Hokay, Silvers seems to indicate that there are potentially three color bands on an agouti, with about 17 different modifying alleles. That makes it about as clear as mud. I always thought there were three bands, black, red/yellow, and brown/gray. While agoutis are a dominant color, it's easy to see that producing the correct type of banding for a show mousie can be quite a complex endeavor. You've raised a question about what I consider to one the the mousery basics, along with nice big PEW's, and I intend to pursue this matter further.

Anybody else have wisdom to share?
 

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Discussion Starter · #3 ·
Hmm, well... there are only two basic hair colours - black and yellow. I've had a look at Silvers' work as well, and think I have some answers, but a lot more questions as well.

Firstly, it appears fairly straightforward that a hair on a mouse can have two or more bands. Agouti hairs have a black base, a yellow middle and a black tip:
Although there are a great number of loci which influence the synthesis of melanin in mice, there are only two loci which control the nature of the pigment formed. Thus the agouti and extension series of alleles determine the relative amount and distribution of yellow pigment (phaeomelanin) and black or brown pigment (eumelanin) in the hairs of the coat.

Mice displaying this phenotype have a typical agouti dorsum, i.e., a unique pattern of pigmentation characterized by a subapical yellow band on an otherwise black (or brown) hair. This black-yellow-black pattern results from a rapid shift from deposition of eumelanin to deposition of phaeomelanin and back again to eumelanin in the hair shaft.

This black-yellow-black pattern results from a rapid shift from deposition of eumelanin to deposition of phaeomelanin and back again to eumelanin in the hair shaft.
So, that's fine. My next question was how it was possible for a dilute (eg chinchilla) to produce a different effect on the base and tips of the hair. My reasoning was that it was the same dilute acting on the same hair colour, therefore the base and tip should match. But they don't.

A hint of an answer is in Silvers' explanation of the structure and composition of the eumelanin in black hair sections:

Regardless of the chromosomal structure of the agouti locus it is apparent that it determines whether eumelanin, phaeomelanin, or both of these pigments are synthesized in the melanocytes of the hair bulb. Moreover, it should be emphasized that these two kinds of pigments are appreciably different from each other when examined under the electron or conventional microscope. When viewed under the latter, yellow granules ... are uniformly round and of approximately the same intensity and size, whereas black granules are much more variable in their characteristics with three different grades of color, four recognizably different shapes, and a wide variation in size.
So, I'm thinking that during the growth of the hair, the eumelanin at the tip, (which emerges first in the growth cycle), may not be the same as that produced in the last phase of the growth of the hair. Therefore, if the two "black" sections are not the same colour, they will be affected to a different degree by the action of a c-dilute such as c(ch).

Does this make sense? What do you think?

I'm still unsure of the hair structure on an argente, for example, which only appears to have a black base and a yellow tip, with the base diluted by pp to slate. So, just two colour sections to the hair, not three?
 

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Yes, other modifiers at other locii determine the arrangement of the color granules, and the location in which the resulting hues are expressed. That almost makes me sound like I know what's going on. I guess it's fair to say I understand in principle if not in the specific. I sometimes wonder, Silvers book being decades old, what we're missing now that the entire mouse genome has been cataloged, and that makes me itch to know more.
 
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